Support importing local workflow templates

[ohltyler]

Description

This PR adds support for importing locally saved workflow templates in JSON or YAML format. A new button is available on the base workflows page, for both the workflows list and the new workflow tabs. When clicked, opens up a modal where users can drag-and-drop or import a template from their local filesystem. The modal will validated and prevent or allow importing, depending on 3 different states:

1. Valid UI template (containing the required workflow fields, + containing ui_metadata field). No warnings, and users can import. Note if this is manually done / misconfigured this may still fail; it is up to the user to not corrupt the values within ui_metadata.
2. Valid template (containing the required workflow fields, but not containing ui_metadata). Warns that the workflow can be imported, but may not be visible from the editor etc. since there is no ui metadata to parse.
3. Invalid template (doesn't contain the required workflow fields, isn't a JSON or YAML file, isn't a parse-able JSON or YAML file, etc.). Tells user the workflow is invalid, blocks any import.

When a user clicks "Import", the plugin attempts to create that workflow on the selected cluster, and is then viewable the same way as any other workflow. Any failures are propagated in a toast message with details, no different than if they were to run the create workflow API directly with the contents of the file.

Demo video showing the 3 different states, and successful importing into the cluster via the modal:

screen-capture.webm

Testing:

• JSON template pulled via export step can be imported and load everything correctly
• YAML templated pulled via export step can be imported and load everything correctly
• non-JSON/non-YAML files are rejected
• format issues with JSON or YAML files are rejected
• workflows with no ui_metadata show correct state
• workflows with valid ui_metadata show correct state

Other minor changes:

• improves spacing on invalid UI workflow state
• helper functions for determining the validity of a workflow template
• moves the create workflow button into a button on the right-hand side on the workflows list page
• minor wording and format updates to headers on the workflows page

Issues Resolved

Makes progress on #66

Check List

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