fix: Anomaly detection features count locked at 5

[quangdutran]

Description

Remove hardcoded maximum features, get the limit from anomaly detection setting API instead

Issues Resolved

Fix #1016

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
• Commits are signed per the DCO using --signoff

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[kaituo]

Thanks for your changes. And sorry for the late response.

Currently, validation fails.

I think this is due to we don't add setting update consumer here: https://github.com/opensearch-project/anomaly-detection/blob/main/src/main/java/org/opensearch/timeseries/rest/RestValidateAction.java#L60-L64

one example: https://github.com/opensearch-project/anomaly-detection/blob/70eb22d02d5d0a68313e68137ffdbf7c030b2a53/src/main/java/org/opensearch/ad/rest/AbstractAnomalyDetectorAction.java#L47

Can you fix backend first?

Also, can you add some IT or UT? IT (cypress tests) can be added here: https://github.com/opensearch-project/opensearch-dashboards-functional-test/tree/main/cypress/integration/plugins/anomaly-detection-dashboards-plugin