[FEATURE] Endpoint to purge cache entries for specific users

[prabhask5]

Description

Finishing previous PR here: #4314

Currently, our system only allows for the invalidation of the entire user authentication cache, which can lead to numerous cache misses and inefficiencies. This change is required to allow for more precise cache management, specifically targeting stale cache entries at the individual user level without disrupting the cache state of other users

Category: New feature
Why these changes are required?
Currently, our system only allows for the invalidation of the entire user authentication cache. This change is required to allow for more precise cache management, specifically targeting stale cache entries at the individual user level without disrupting the cache state of other users.
What is the old behavior before changes and new behavior after changes?
Previously, invalidating a user's cache required clearing the entire cache, affecting all users. The new behavior introduces an endpoint that allows for the invalidation of cache entries on a per-user basis, thereby maintaining cache integrity for other users and reducing unnecessary cache misses.

Issues Resolved

#2829

Is this a backport? If so, please add backport PR # and/or commits #
no

Do these changes introduce new permission(s) to be displayed in the static dropdown on the front-end? If so, please open a draft PR in the security dashboards plugin and link the draft PR here

Testing

Unit testing was written in FlushCacheApiTest.java

Check List

• New functionality includes testing
• New functionality has been documented
• New Roles/Permissions have a corresponding security dashboards plugin PR
• API changes companion pull request created
• Commits are signed per the DCO using --signoff

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[cwperks]

@prabhask5 Can you please include the commits from @dlin2028 so that he is also credited with this contribution as well? I want to make sure that @dlin2028's work also gets acknowledged for this contribution.