rgw: make keystone work without admin token(service ac requirement)

rgw: make keystone work without admin token(service ac requirement)

Ceph RGW admin credentials must not be a requirement.
Both ec2 auth and keystone token validation work without an admin token.

And the user token verification will use its own token. The only
requirement for the service admin user token is the allow_expired, but
in our case we don't use this parameter.

fixes: https://tracker.ceph.com/issues/68327

Co-authored-by: @kayrus
Signed-off-by: Deepika Upadhyay <deepika.upadhyay@clyso.com>