[Painless Lab] Moving out of Beta

[jloleysens]

Summary

With #57538 merged, this meta issue will be used for tracking any additional feedback or work needed for moving Painless Lab out of beta.

Current items to address

After we have worked through these items we should be able to remove the beta. They are listed in order of importance (determined by the amount of work and the potential value it will contribute).

Check off each item as we address them and add a link to any PR related to addressing the work.

Features

• Prepopulate index-selection field with a list of available indices. We also want to create a flyout that lets you preview the mappings of each index to help you select the one you want.
• The parameters field should be a component that lets you add key-value pairs via a list editor. There can be a button that lets you switch back and forth between the KV list mode and JSON editing mode.
• Syntax checking and highlighting for JSON text editors and implement regex syntax highlighting in Painless editor (per Create Painless Lab app #57538 (comment))
• Allow the user to opt out of live updating and use a "Submit" button instead, per Refine Painless Playground UI/UX kertal/kibana#5 (comment)

Fixes

• Improve error message reporting under certain conditions
  (Create Painless Lab app #57538 (comment))
• Investigate layout issue per 👉🏻 Create Painless Lab app #57538 (comment)
• Move help into the main Kibana header bar help menu (see screenshot below)

Tests and docs

• Add a page to the Elastic docs
• Add API integration tests for the execute endpoint. Check that, for instance, invalid Painless still returns 200 with error details as opposed to 400.
• Add Jest component integration tests (or at least a smoke test for the main container)
• Create a test rail plan

Other

One interesting suggestion mentioned in the original painless lab pr: #57538 (comment). Provide user feedback inline rather than in a separate, always on, output area.

[elasticmachine]

Pinging @elastic/es-ui (Team:Elasticsearch UI)

[elasticmachine]

Pinging @elastic/kibana-management (Team:Kibana Management)