feat(replication): Add support for read replica replication

[iambriccardo]

Summary

Adds support for running ETL logical replication from a PostgreSQL physical read replica.

This includes:

• optional store_pg_connection config so replication/table copy can read from a standby while PostgresStore writes state to a writable endpoint
• source migration startup that skips migration execution when the configured source is in recovery
• local Docker Compose read-replica setup using pg_basebackup and a physical replication slot
• xtask/nextest sharding updates to start and pass matching primary/replica ports
• read-replica integration tests covering replica replay, initial copy + CDC, and idle slot advancement
• docs for configuring Postgres read replicas and PostgreSQL 16+ requirements

[coveralls]

coverage: 72.965% (-0.001%) from 72.966% — add-read-replica-support into main