Wrapped pgx

Wrapped pgx is a simple wrap on the PostgreSQL driver library pgx. It is used by sqlc, providing telementry for generated code.

Components:

• Pool: a wrapper of pgxpool.Pool. It manages a set of connection pools, including a primary pool and a set of replica pools. We assume replica pools are heterogeneous read-only replicas, meaning some replicas can be a partial copy of the primary database, using logical replication.
• WConn: a connection wrapper, implementing "WGConn".
• WTx: a transaction wrapper, implementing "WGConn".