Testcontainers-java: Add support for gcloud emulators

[eddumelendez]

google cloud sdk is available via docker hub. I think testcontainers can provide an easy way to start emulators like pubsub, datastore, firestore, spanner.

If you agreed, I can work on it.

[rnorth]

Yes please! I'd use this myself 😄

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. If you believe this is a mistake, please reply to this comment to keep it open. If there isn't one already, a PR to fix or at least reproduce the problem in a test case will always help us get back on track to tackle this.

[saturnism]

for record, this being implemented by @eddumelendez in #2690

[eddumelendez]

2690 is merged!