[Backport 2.x] Alerting Enhancements: Alerting Comments (Experimental) (#1561)

[toepkerd]

• initial commit, functional but needs refactoring

• refactored QueryLevelTriggerExecutionContext to not need both Alert and AlertContext field, but only AlertContext field

• misc additions and fixes

• misc cleanup

• misc changes and basic ITs

• cleanup

• renaming notes to comments

• misc changes

• changed API endpoints

• more misc changes and fixes

• misc cleanup

• updated a comment

• misc cleanup and setting refresh policy to immediate

• fixed lint issues and other restructuring

• review-based changes

• update after adding entityType to Comment model

• misc fixes

• removing comments history enabled setting

• adding release notes

• IT fixes

• removing dev code vestiges

• changing logger calls

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[toepkerd]

As per this comment, CI Failures will be addressed at a later time: https://github.com/opensearch-project/alerting/pull/1561#issuecomment-2161864713. The failing tests, latest error is not lost when alert is completed and test alert completion are the same ones failing in the original PR.