Create Admin CRUD Endpoints for Visa - Permission Mapping

[Buwujiu]

Detailed Description

Implement endpoints:

1. Get mappings by visa Id
2. Get mappings by policy Id, just the policy, not the mask
3. 1 endpoint to update or create visa permissions, 1 visa - many permissions.

• each visa should only have 1 entry per policy, example: SONG. READ, if the request is to update to SONG.WRITE, then update it to be SONG.WRITE, do not keep both.

4. 1 endpoint to remove mappings by VISA id AND policy name(or ID? as long as it's consistent with the rest of the API). 1 visa - many policies.

All endpoints:

• Only accessible to admins.
• should have pagination
• should have basic error handling