Add REST endpoints to tag and untag policies in bulk

[sahibamittal]

Description

Adds the new endpoints:

• POST /api/v1/tag/{name}/policy
• DELETE /api/v1/tag/{name}/policy

And deprecates the redundant endpoints:

• POST /api/v1/policy/{uuid}/tag/{name}
• DELETE /api/v1/policy/{uuid}/tag/{name}

Checklist

• I have read and understand the contributing guidelines
• This PR fixes a defect, and I have provided tests to verify that the fix is effective
• This PR implements an enhancement, and I have provided tests to verify that it works as intended
• This PR introduces changes to the database model, and I have updated the migration changelog accordingly
• This PR introduces new or alters existing behavior, and I have updated the documentation accordingly