[ML] AIOps: Fix relative time bound support in the chart preview

[darnautov]

Summary

• Fixes relative time range support in the Change Point Detection UI.
• Enables functional tests (resolves Failing test: Chrome X-Pack UI Functional Tests - aiops.x-pack/test/functional/apps/aiops/change_point_detection·ts - aiops change point detection shows multiple results when split field is selected #158851)

Checklist

• Unit or functional tests were updated or added to match the most common scenarios

[elasticmachine]

Pinging @elastic/ml-ui (:ml)

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: e75636c

Metrics [docs]

Async chunks

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

id	before	after	diff
aiops	805.3KB	805.3KB	+4.0B

Unknown metric groups

ESLint disabled line counts

id	before	after	diff
enterpriseSearch	13	15	+2
securitySolution	411	415	+4
total			+6

Total ESLint disabled count

id	before	after	diff
enterpriseSearch	14	16	+2
securitySolution	492	496	+4
total			+6

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

cc @darnautov

[darnautov]

Checking with the flaky test runner https://buildkite.com/elastic/kibana-flaky-test-suite-runner/builds/2437

50/50 🟢

[peteharverson]

Tested and LGTM

[kibanamachine]

💔 All backports failed

Status	Branch	Result
❌	8.10	The branch "8.10" does not exist

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Friendly reminder: Looks like this PR hasn’t been backported yet.
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