[Feature Request] Native GCP Receiver (Pub/Sub or Spanner)

[alfredomusumeci]

Hello,

I've noticed Alertmanager provides native receivers for several services, and that many users in AWS environments often leverage native SNS. In our environment, we rely heavily on Google Cloud and would benefit from an officially supported, native GCP receiver.

We were primarily thinking of Spanner support for resiliency reasons, though I understand it isn't a classic notification sink. In that case, we'd be open to using Pub/Sub also.

Questions:

• Would you be open to a PR for either scenario?

Thanks,
Fred