Implement plugin documentation generator (#86)

Co-authored-by: traut <[email protected]>

.github/styles/config/vocabularies/fabric-vocab/accept.txt

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 GitHub
 Fabric
 boolean
+namespace

docs/plugins/_index.md

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+---
+title: Plugins
+type: docs
+weight: 5
+---
+
+# Plugins
+
+Fabric relies on plugins to implement data sources and content providers. To utilise a plugin's data sources and content providers, it must be installed by Fabric. The global configuration should specify all required plugins (see [Global configuration]({{< ref "../language/configs.md/#global-configuration" >}}) for the details). Additionally, some data sources and content providers require configuration (for example, API keys, URLs, credentials, etc).
+
+A plugin name consists of a namespace (a name of a plugin vendor) and a short name. For example, `blackstork/elasticsearch` plugin implements Elasticsearch client data source and is released by [BlackStork](https://blackstork.io).
+
+## Where to get the plugins
+
+Plugins are released and distributed independently from Fabric, with their own release cycle and version.
+You can find a list of plugins released by BlackStork at the [Releases page](https://github.com/blackstork-io/fabric/releases) in Fabric GitHub.

docs/plugins/builtin.md

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+---
+title: Built-in
+weight: 10
+type: docs
+---
+
+# Built-in data sources and content providers
+
+`fabric` binary includes a set of built-in data sources and content providers, available out-of-the-box.
+
+## Data sources
+
+### `csv`
+
+#### Configuration
+
+The data source supports the following configuration parameters:
+
+```hcl
+config data csv {
+    delimiter = <string>  # optional
+}
+```
+
+#### Usage
+
+The data source supports the following parameters in the data blocks:
+
+```hcl
+data csv {
+    path = <string>  # required
+}
+```
+
+### `inline`
+
+#### Configuration
+
+The data source doesn't support configuration.
+
+#### Usage
+
+The data source doesn't define any parameters in the `data` block.
+
+### `json`
+
+#### Configuration
+
+The data source doesn't support configuration.
+
+#### Usage
+
+The data source supports the following parameters in the data blocks:
+
+```hcl
+data json {
+    glob = <string>  # required
+}
+```
+
+### `txt`
+
+#### Configuration
+
+The data source doesn't support configuration.
+
+#### Usage
+
+The data source supports the following parameters in the data blocks:
+
+```hcl
+data txt {
+    path = <string>  # required
+}
+```
+
+## Content providers
+
+### `frontmatter`
+
+#### Configuration
+
+The content provider doesn't support configuration.
+
+#### Usage
+
+The content source supports the following parameters in the content blocks:
+
+```hcl
+content frontmatter {
+    content = <map of dynamic>  # optional
+    format = <string>  # optional
+}
+```
+
+### `image`
+
+#### Configuration
+
+The content provider doesn't support configuration.
+
+#### Usage
+
+The content source supports the following parameters in the content blocks:
+
+```hcl
+content image {
+    alt = <string>  # optional
+    src = <string>  # required
+}
+```
+
+### `list`
+
+#### Configuration
+
+The content provider doesn't support configuration.
+
+#### Usage
+
+The content source supports the following parameters in the content blocks:
+
+```hcl
+content list {
+    format = <string>  # optional
+    item_template = <string>  # required
+}
+```
+
+### `table`
+
+#### Configuration
+
+The content provider doesn't support configuration.
+
+#### Usage
+
+The content source supports the following parameters in the content blocks:
+
+```hcl
+content table {
+    columns = <list of object>  # required
+}
+```
+
+### `text`
+
+#### Configuration
+
+The content provider doesn't support configuration.
+
+#### Usage
+
+The content source supports the following parameters in the content blocks:
+
+```hcl
+content text {
+    absolute_title_size = <number>  # optional
+    code_language = <string>  # optional
+    format_as = <string>  # optional
+    text = <string>  # required
+}
+```

docs/plugins/elasticsearch.md

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+---
+title: blackstork/elasticsearch
+weight: 20
+type: docs
+---
+
+# `blackstork/elasticsearch` plugin
+
+## Installation
+
+To install the plugin, add it to `plugin_versions` map in the Fabric global configuration block (see [Global configuration]({{< ref "configs.md#global-configuration" >}}) for more details), with a version constraint restricting which available versions of the plugin the codebase is compatible with:
+
+```hcl
+fabric {
+  plugin_versions = {
+    "blackstork/elasticsearch" = "=> v0.0.0-dev"
+  }
+}
+```
+
+## Data sources
+
+The plugin has the following data sources available:
+
+### `elasticsearch`
+
+#### Configuration
+
+The data source supports the following configuration parameters:
+
+```hcl
+config data elasticsearch {
+    api_key = <list of string>  # optional
+    api_key_str = <string>  # optional
+    base_url = <string>  # required
+    basic_auth_password = <string>  # optional
+    basic_auth_username = <string>  # optional
+    bearer_auth = <string>  # optional
+    ca_certs = <string>  # optional
+    cloud_id = <string>  # optional
+}
+```
+
+#### Usage
+
+The data source supports the following parameters in the data blocks:
+
+```hcl
+data elasticsearch {
+    fields = <list of string>  # optional
+    id = <string>  # optional
+    index = <string>  # required
+    query = <map of dynamic>  # optional
+    query_string = <string>  # optional
+}
+```

docs/plugins/github.md

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+---
+title: blackstork/github
+weight: 20
+type: docs
+---
+
+# `blackstork/github` plugin
+
+## Installation
+
+To install the plugin, add it to `plugin_versions` map in the Fabric global configuration block (see [Global configuration]({{< ref "configs.md#global-configuration" >}}) for more details), with a version constraint restricting which available versions of the plugin the codebase is compatible with:
+
+```hcl
+fabric {
+  plugin_versions = {
+    "blackstork/github" = "=> v0.0.0-dev"
+  }
+}
+```
+
+## Data sources
+
+The plugin has the following data sources available:
+
+### `github_issues`
+
+#### Configuration
+
+The data source supports the following configuration parameters:
+
+```hcl
+config data github_issues {
+    github_token = <string>  # required
+}
+```
+
+#### Usage
+
+The data source supports the following parameters in the data blocks:
+
+```hcl
+data github_issues {
+    assignee = <string>  # optional
+    creator = <string>  # optional
+    direction = <string>  # optional
+    labels = <list of string>  # optional
+    limit = <number>  # optional
+    mentioned = <string>  # optional
+    milestone = <string>  # optional
+    repository = <string>  # required
+    since = <string>  # optional
+    sort = <string>  # optional
+    state = <string>  # optional
+}
+```

docs/plugins/graphql.md

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+---
+title: blackstork/graphql
+weight: 20
+type: docs
+---
+
+# `blackstork/graphql` plugin
+
+## Installation
+
+To install the plugin, add it to `plugin_versions` map in the Fabric global configuration block (see [Global configuration]({{< ref "configs.md#global-configuration" >}}) for more details), with a version constraint restricting which available versions of the plugin the codebase is compatible with:
+
+```hcl
+fabric {
+  plugin_versions = {
+    "blackstork/graphql" = "=> v0.0.0-dev"
+  }
+}
+```
+
+## Data sources
+
+The plugin has the following data sources available:
+
+### `graphql`
+
+#### Configuration
+
+The data source supports the following configuration parameters:
+
+```hcl
+config data graphql {
+    auth_token = <string>  # optional
+    url = <string>  # required
+}
+```
+
+#### Usage
+
+The data source supports the following parameters in the data blocks:
+
+```hcl
+data graphql {
+    query = <string>  # required
+}
+```