Add deferrable GCSObjectExistenceSensorAsync

[rajaths010494]

This PR donates the following developed GCSObjectExistenceSensorAsync` in astronomer-providers repo to apache airflow.

GCSObjectExistenceSensorAsync

[rajaths010494]

When i re-requested for review. It automatically removed reviewers and now i am not able to add them back.
@mik-laj @turbaszek

[vchiapaikeo]

Hi @rajaths010494 @kaxil - I wanted to point out a possible bug that is introduced here - it seems like using this approach:

    async def get_storage_client(self, session: ClientSession) -> Storage:
        """Returns a Google Cloud Storage service object."""
        with await self.service_file_as_context() as file:
            return Storage(service_file=file, session=cast(Session, session))

does not honor the impersonation_chain when application default credentials (ADC) are being used. We've tried a similar approach from astronomer-providers and encountered issues on our end. I believe this is because in the case that await self.service_file_as_context() as file yields None (the fall through here), the async storage client gets instantiated with this:

return Storage(service_file=None, session=cast(Session, session))

TalkIQ's async io storage client has no idea of the impersonation chain on instantiation here --> https://github.com/talkiq/gcloud-aio/blob/4e0006240913ecadde68722b8986f184a9b1adea/storage/gcloud/aio/storage/storage.py#L149-L168

And as a result, the token gets instantiated with ADC without regard for impersonation chain.

Edit: On second look, it seems like provide_gcp_credential_file_as_context does not honor the impersonation chain at all? Compare this with get_credentials_and_project_id which handles the impersonation chain properly

[rajaths010494]

Thanks @vchiapaikeo i will look at this and check get_credentials_and_project_id which handles the impersonation chain properly.
and add support for impersonation chain.
Edit - As you mentioned currently gclou-aio-storage doesn't yet have support for it.
Once there is a support for it will add support for it. Until then it will be a limitation.