[ML] AIOps: Move log pattern analysis fetch code to common to be available via server

[walterra]

Summary

Follow up to #167237.
Part of #167467.

We plan to reuse some of the queries log pattern analysis does to use via log rate analysis too. Log pattern analysis mostly does queries from the client side, log rate analysis has its own API endpoint and does ES queries via Kibana server. In preparation for the use via log rate analysis, this moves the code we need to have available server side for log rate analysis to the common area of the plugin so it can be used both on server/client.

Checklist

• Unit or functional tests were updated or added to match the most common scenarios
• This was checked for breaking API changes and was labeled appropriately

[elasticmachine]

Pinging @elastic/ml-ui (:ml)

[jgowdyelastic]

Tested, LGTM

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: b3b251f

Metrics [docs]

Module Count

Fewer modules leads to a faster build time

id	before	after	diff
aiops	476	480	+4

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
aiops	594.0KB	594.0KB	+37.0B

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

cc @walterra