Split up plugin dev docs from team docs. Add some welcome landing pages

dev_docs/api_welcome.mdx

@@ -0,0 +1,15 @@
+---
+id: kibDevDocsApiWelcome
+slug: /kibana-dev-docs/api-welcome
+title: Kibana plugin API documentation
+summary: The home of automatically generated plugin API documentation using extracted TSDocs
+date: 2021-01-02
+tags: ['kibana','dev', 'contributor', 'api docs']
+---
+
+Welcome to Kibana's plugin API documentation. As a plugin developer, this is where you can 
+learn the details of every service you can take advantage of, to help you build awe-inspiring, creative solutions and applications!
+
+If you have any questions or issues, please reach out to the Kibana platform team or create an issue [here](https://github.com/elastic/kibana/issues).
+
+

dev_docs/dev_welcome.mdx

@@ -0,0 +1,17 @@
+---
+id: kibDevDocsWelcome
+slug: /kibana-dev-docs/welcome
+title: Kibana plugin developer documentation
+summary: Build custom solutions and applications on top of Kibana.
+date: 2021-01-02
+tags: ['kibana','dev', 'contributor']
+---
+
+Welcome to Kibana's plugin developer documentation!
+
+Did you know that the vast majority of functionality built inside of Kibana is a plugin? A handful of core services hold the system together,
+but it's our vast system of plugin developers that provide amazing, out of the box functionality, you can use when building your own set of
+custom utilities and applications.
+
+Browse the `Services` section to view all the plugins that offer functionality you can take advantage of, or check out the
+`API documentation` to dig into the nitty gritty details or every public plugin API.

src/plugins/data/README.mdx

@@ -1,6 +1,6 @@
 ---
 id: kibDataPlugin
-slug: /kibana-dev-guide/services/data-plugin
+slug: /kibana-dev-docs/services/data-plugin
 title: Data services
 image: https://source.unsplash.com/400x175/?Search
 summary: The data plugin contains services for searching, querying and filtering.