Added support to add client role on service account user

[zikphil]

This is a gross copy/paste of PR #202 but to also add the capability of adding Client Role to Client Service Account.

Example Use-Case: Grant realm-management roles on another client's service account.

Apologies for the dirtyness of code, this is my first Go coding experience.

resource "keycloak_openid_client_service_account_client_role" "client_service_account_roles" {
  realm_id = keycloak_realm.test-realm.id
  client_id  = data.keycloak_openid_client.realm_management.id
  service_account_user_id  = keycloak_openid_client.test_client.service_account_user_id
  role = "manage-realm"
}

[waldemarschmalz]

It is already possible to add client roles to a service account user. See example/main.tf :-)

[zikphil]

Omg you are absolutely right