Discuss usage with managed Postgres on GCP [DBZ-3761]

Migrated from [DBZ-3761](https://issues.redhat.com/browse/DBZ-3761)

Recently, Managed Postgres on GCP gained support for logical decoding, meaning Debezium can be used with it. See [this post|https://daily.dev/blog/building-a-fault-tolerant-event-driven-architecture-with-google-cloud-pulumi-and-debezium] for details.

We discuss usage with other PG cloud services [here|https://debezium.io/documentation/reference/connectors/postgresql#postgresql-in-the-cloud], so we should add a section on the GCP service, too.

Start with the PostgreSQL connector documentation at debezium.io/documentation/reference/connectors/postgresql#postgresql-in-the-cloud and review how the existing cloud-service sections are structured. Add a section covering Managed Postgres on GCP and its logical-decoding usage, with the linked post as context; done means the GCP service is documented alongside the other PostgreSQL cloud services.

Written by the indexing model from the issue text.