docs: add coming-soon public API test endpoints (APP-1552)

[MikaKerman]

Summary

• Documents the planned M2 public API surface (tests, latest test executions, per-test execution history) so Elastic can review the contract before the routes exist.
• Six hand-written list/get pages with a Coming soon callout. No openapi: frontmatter and no fake OpenAPI paths, so the playground cannot 404.
• Intro table, tests overview, incremental-sync note, and tests view-scope on authentication. Nav groups in docs.json.

Linear: APP-1552

When the API ships, replace these pages with generated OpenAPI stubs (same pattern as columns).

Test plan

• Mintlify preview: Tests / Latest test executions / Test executions groups appear in the API Reference sidebar
• Each of the six pages shows the Coming soon warning and example JSON
• Intro “What you can read” lists the three coming-soon rows
• No “Try it” playground on these pages (no OpenAPI binding)
• Existing asset/column/lineage pages still generate from OpenAPI

Made with Cursor

[linear]

APP-1552

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