PostgreSQL replication provider

[renecannao]

PostgreSQL Provider

Build on the database abstraction layer (PR #41) to add PostgreSQL streaming replication support.

Scope

• Implement DatabaseProvider interface for PostgreSQL
• Support PostgreSQL streaming replication discovery
• Support PostgreSQL failover (promote standby, reconfigure replication)
• LSN-based replication position tracking
• Integration with Patroni-style failover patterns

Prerequisites

• Database provider interface is already in place (go/inst/provider.go)
• MySQL provider serves as reference implementation (go/inst/provider_mysql.go)

Considerations

• PostgreSQL replication model differs significantly from MySQL (WAL-based, not binlog)
• Replication slots, synchronous/asynchronous replication modes
• pg_stat_replication for monitoring
• Consider read-only routing through PgBouncer (similar to ProxySQL for MySQL)