Implements an LLM-based root cause analysis process. At a high level, it
works by investigating entities - which means pulling in alerts, SLOs,
and log patterns. From there, it can inspect related entities to get to
the root cause.

The backend implementation lives in
`x-pack/packages/observability_utils-*` (`service_rca`). It can be
imported into any server-side plugin and executed from there.

The UI changes are mostly contained to
`x-pack/plugins/observability_solution/observabillity_ai_assistant_app`.
This plugin now exports a `RootCauseAnalysisContainer` which takes a
stream of data that is returned by the root cause analysis process.

The current implementation lives in the Investigate app. There, it calls
its own endpoint that kicks off the RCA process, and feeds it into the
`RootCauseAnalysisContainer` exposed by the Observability AI Assistant
app plugin. I've left it in a route there so the investigation itself
can be updated as the process runs - this would allow the user to close
the browser and come back later, and see a full investigation.

> [!NOTE]
> Notes for reviewing teams
>
> @kbn/es-types:
> - support both types and typesWithBodyKey
> - simplify KeysOfSources type
>
> @kbn/server-route-repository:
> - abortable streamed responses
>
> @kbn/sse-utils*:
> - abortable streamed responses
> - serialize errors in specific format for more reliable re-hydration
of errors
> - keep connection open with SSE comments
>
> @kbn/inference-*:
> - export *Of variants of types, for easier manual inference
> - add automated retries for `output` API
> - add `name` to tool responses for type inference (get type of tool
response via tool name)
> - add `data` to tool responses for transporting internal data (not
sent to the LLM)
> - simplify `chunksIntoMessage`
> - allow consumers of nlToEsql task to add to `system` prompt
> - add toolCallId to validation error message
>
> @kbn/aiops*:
> - export `categorizationAnalyzer` for use in observability-ai*
>
> @kbn/observability-ai-assistant*
> - configurable limit (tokens or doc count) for knowledge base recall
>
> @kbn/slo*:
> - export client that returns summary indices

---------

Co-authored-by: kibanamachine <42973632+kibanamachine@users.noreply.github.com>
Co-authored-by: Maryam Saeidi <maryam.saeidi@elastic.co>
Co-authored-by: Bena Kansara <bena.kansara@elastic.co>
(cherry picked from commit fa1998c)

# Conflicts:
#	.github/CODEOWNERS