As part of the `OS-FEDERATION` keystone extension has added a `mappings` api. Add support for it. [docs](https://docs.openstack.org/api-ref/identity/v3-ext/index.html#os-federation-api) [code](https://github.com/openstack/keystone/blob/stable/yoga/keystone/api/os_federation.py#L248) - [x] List mappings - [x] Create mapping - [x] Get mapping - [x] Update mapping - [x] Delete mapping