Implement jwt decode for Azure auth manager

Currently when trying to use Azure oauth token to get an API key, Galaxy will raise a NotImplementedError. This is due to decode_user_access_token not being implemented in psa_authnz.py which is the auth manager used for Azure. This method should be implemented in that file, similar to how it is implemented in custos_authnz.py. This should also be raised as an issue upstream, but for now we can implement it for our build of Galaxy.