Have both 401 and 403 for `Unauthorized` errors over different endpoints - we should consolidate

[rishabh-bhargava]

Example 401: https://github.com/togethercomputer/openapi/blob/main/openapi.yaml#L46

Example 403: https://github.com/togethercomputer/openapi/blob/main/openapi.yaml#L908

403 is typically Forbidden, which is when a user is authenticated, but not authorized for that particular resource (for ex: non-admin user trying to access an admin resource)