Use keycloak_realm as default for sub-entities

[guidograzioli]

Default realm for entities like federation or client to keycloak_realm top-level variable when the dictionary key is not defined. This allows to reduce:

  roles:
    - role: middleware_automation.keycloak.keycloak_realm
      keycloak_realm: TestRealm
      keycloak_clients:
        - name: TestClient1
          client_id: TestClient1
          realm: TestRealm
          users:
            - username: TestUser
              password: password
              client_roles:
                - client: TestClient1
                  role: TestClient1User
                  realm: TestRealm

to:

  roles:
    - role: middleware_automation.keycloak.keycloak_realm
      keycloak_realm: TestRealm
      keycloak_clients:
        - name: TestClient1
          client_id: TestClient1
          users:
            - username: TestUser
              password: password
              client_roles:
                - client: TestClient1
                  role: TestClient1User

Fix #179