@darshan-majithiya had opened #15429 to add the hyperparameter tuning PR but it's gone stale. I'm adding this issue to see if they want to pick it back up, or if not, if someone wants to pick up where they left off in the spirit of open source 😄 
airflow/providers/google/cloud/operators/mlengine.py
the Service Account Token Creator IAM role.
        If set as a sequence, the identities from the list must grant
        Service Account Token Creator IAM role to the directly preceding identity, with first
        account from the list granting this role to the originating account (templated).
    :type impersonation_chain: Union[str, Sequence[str]]
    """
    template_fields = [
        '_project_id',
        '_model_name',
        '_impersonation_chain',
    ]
    def __init__(
        self,
        *,
        model_name: str,
        delete_contents: bool = False,
        project_id: Optional[str] = None,
        gcp_conn_id: str = 'google_cloud_default',
        delegate_to: Optional[str] = None,
        impersonation_chain: Optional[Union[str, Sequence[str]]] = None,
        **kwargs,
    ) -> None:
        super().__init__(**kwargs)
        self._project_id = project_id
        self._model_name = model_name
        self._delete_contents = delete_contents
        self._gcp_conn_id = gcp_conn_id
        self._delegate_to = delegate_to
        self._impersonation_chain = impersonation_chain
    def execute(self, context):