[8.x][Obs AI Assistant] Serverless API integration tests (#192219)

[neptunian]

Tests for serverless

• copies over and modifies all tests from stateful to work in serverless. deployment agnostic tests do not yet support enterprise license for stateful, so are tests don't yet qualify as being deployment agnostic. Given how difficult it is to see differences from the stateful tests, I've added PR comments where I've changed something that might be of interest.
• changes to createObservabilityAIAssistantApiClient to use supertest without basic auth and accept headers for serverless and use roles
• removes creating persisted users when tests start and use roles within tests. its not possible to create custom users with the serverless test framework at the moment. See
  [Obs AI Assistant] Serverless tests should use cookie based auth instead of api keys for internal routes #192711

Skipped tests

• knowledge base tests [Obs AI Assistant] fix knowledge base tests failing in serverless #192886
• any test suite that uses the LLM proxy has been skipped on MKI [Obs AI Assistant] Fix tests using Llm proxy in serverless #192751
• all tests that depend on the config.modelId skipped in MKI [Obs AI Assistant] Update knowledge base setup route to accept a model id #192757

TODO:

• move over remaining tests
• test in MKI environment before merging
• create issues for skipped tests
• this will not run on MKI (after merging) unless we ping the appex-qa team to add it to the pipeline. this is due to creating a separate config. ask appex-qa team to add our config.

Followup / related issues to be tracked in a newly created issue:

• [Obs AI Assistant] Update knowledge base setup route to accept a model id #192757
• [Obs AI Assistant] fix knowledge base tests failing in serverless #192886
• [Obs AI Assistant] Fix tests using Llm proxy in serverless #192751
• [Obs AI Assistant] Fetch user instructions using id instead of username for knowledge base instructions #192701
• [Obs AI Assistant] unskip summarize tests #192497
• [Obs AI Assistant] Serverless tests should use cookie based auth instead of api keys for internal routes #192711
• [Obs AI Assistant] Deployment agnostic API integration tests #192718
• serverless functional tests
• inquire with ml-ui-team to have the ability to delete system indices which we do after uninstalling tiny elser with .ml indices

Summary

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Checklist

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• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• Documentation was added for features that require explanation or tutorials
• Unit or functional tests were updated or added to match the most common scenarios
• Flaky Test Runner was used on any tests changed
• Any UI touched in this PR is usable by keyboard only (learn more about keyboard accessibility)
• Any UI touched in this PR does not create any new axe failures (run axe in browser: FF, Chrome)
• If a plugin configuration key changed, check if it needs to be allowlisted in the cloud and added to the docker list
• This renders correctly on smaller devices using a responsive layout. (You can test this in your browser)
• This was checked for cross-browser compatibility

Risk Matrix

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Before closing this PR, invite QA, stakeholders, and other developers to identify risks that should be tested prior to the change/feature release.

When forming the risk matrix, consider some of the following examples and how they may potentially impact the change:

Risk	Probability	Severity	Mitigation/Notes
Multiple Spaces—unexpected behavior in non-default Kibana Space.	Low	High	Integration tests will verify that all features are still supported in non-default Kibana Space and when user switches between spaces.
Multiple nodes—Elasticsearch polling might have race conditions when multiple Kibana nodes are polling for the same tasks.	High	Low	Tasks are idempotent, so executing them multiple times will not result in logical error, but will degrade performance. To test for this case we add plenty of unit tests around this logic and document manual testing procedure.
Code should gracefully handle cases when feature X or plugin Y are disabled.	Medium	High	Unit tests will verify that any feature flag or plugin combination still results in our service operational.
See more potential risk examples

For maintainers

• This was checked for breaking API changes and was labeled appropriately

[elasticmachine]

Pinging @elastic/obs-ai-assistant (Team:Obs AI Assistant)

[kibana-ci]

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Metrics [docs]

✅ unchanged

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