…ream (#63092)

Adds a new `postgreSQL.logicalReplication` configuration to allow MSP to
generate prerequisite setup for integration with Datastream:
https://cloud.google.com/datastream/docs/sources-postgresql. Integration
with Datastream allows the Data Analytics team to self-serve data
enrichment needs for the Telemetry V2 pipeline.

Enabling this feature entails downtime (Cloud SQL instance restart), so
enabling the logical replication feature at the Cloud SQL level
(`cloudsql.logical_decoding`) is gated behind
`postgreSQL.logicalReplication: {}`.

Setting up the required stuff in Postgres is a bit complicated,
requiring 3 Postgres provider instances:

1. The default admin one, authenticated with our admin user
2. New: a workload identity provider, using
cyrilgdn/terraform-provider-postgresql#448 /
sourcegraph/managed-services-platform-cdktf#11.
This is required for creating a publication on selected tables, which
requires being owner of said table. Because tables are created by
application using e.g. auto-migrate, the workload identity is always the
table owner, so we need to impersonate the IAM user
3. New: a "replication user" which is created with the replication
permission. Replication seems to not be a propagated permission so we
need a role/user that has replication enabled.

A bit more context scattered here and there in the docstrings.

Beyond the Postgres configuration we also introduce some additional
resources to enable easy Datastream configuration:

1. Datastream Private Connection, which peers to the service private
network
2. Cloud SQL Proxy VM, which only allows connections to `:5432` from the
range specified in 1, allowing a connection to the Cloud SQL instance
2. Datastream Connection Profile attached to 1

From there, data team can click-ops or manage the Datastream Stream and
BigQuery destination on their own.

Closes CORE-165
Closes CORE-212

Sample config:

```yaml
  resources:
    postgreSQL:
      databases:
        - "primary"
      logicalReplication:
        publications:
          - name: testing
            database: primary
            tables:
              - users
```

## Test plan

sourcegraph/managed-services#1569

## Changelog

- MSP services can now configure `postgreSQL.logicalReplication` to
enable Data Analytics team to replicate selected database tables into
BigQuery.