Implement GKEStartPodOperatorAsync

[raphaelauv]

GKEStartPodOperator is a useful operator that retrieve at every run the config_file of a GKE thanks to gcloud cli

so you don't need to manage the update of :

• a K8S config_file
  or
• a airflow connection kubernetes_conn_id

Having a GKEStartPodOperatorAsync would be great

[raphaelauv]

look like it would be necessary to edit the GKEStartPodOperator to move all the content of execute in a separate function load_gke_context

so we could write :

GKEStartPodOperatorAsync(KubernetesPodOperatorAsync)

    ...

    def execute(self, context: 'Context') -> Optional[str]:
        GKEStartPodOperator.load_gke_context(context)
        return super().execute(context)