[OBSERVABILITY][ResponseOps][Cases][8.19] Note about new case analytics indices

[nastasha-solomon]

⚠️ NOTE: Must be merged after elastic/kibana#229041. ⚠️

Description

Added note letting users know that it's possible to to visualize data from cases in your space. Also added a limitations section and updated it so it matches what's included in other case docs.

Documentation sets edited in this PR

Check all that apply.

• Stateful (docs/en/observability/*)
• Serverless (docs/en/serverless/*)
• Integrations Developer Guide (docs/en/integrations/*)
• None of the above

Related issue

Closes elastic/docs-content#1716

Checklist

• Product/Engineering Review
• Writer Review

Follow-up tasks

Select one.

• This PR does not need to be ported to another doc set because:
  • The concepts in this PR only apply to one doc set (serverless or stateful)
  • The PR contains edits to both doc sets (serverless and stateful)
• This PR needs to be ported to another doc set:
  • Port to stateful docs: [DOCS][ResponseOps][Cases][8.19] New case analytics indices feature and schema docs kibana#229041
  • Port to serverless docs: [Cases][9.2] Cases as data feature docs docs-content#2220 and [DOCS][Cases][9.2] Case analytics indices schema kibana#229036 and

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[nastasha-solomon]

The CI checks for this PR will fail until elastic/kibana#229041 is merged.

[nastasha-solomon]

Not being released in 8.x.