[8.1] [Response Ops][Cases] Fetch alerts within observability (#123883)

[kibanamachine]

Backport

This is an automatic backport to 8.1 of:

• [Response Ops][Cases] Fetch alerts within observability #123883

Questions ?

Please refer to the Backport tool documentation

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: 282a965
• Storybooks Preview
• Webpack Bundle Analyzer

Metrics [docs]

Module Count

Fewer modules leads to a faster build time

id	before	after	diff
observability	350	353	+3

Async chunks

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

id	before	after	diff
cases	294.9KB	294.9KB	+42.0B
observability	391.0KB	392.1KB	+1.0KB
total			+1.1KB

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

cc @jonathan-buttner