Add PGMQ support / broker #662

Is your feature request related to a problem?

Existing Postgres brokers for taskiq use custom tables + LISTEN/NOTIFY. PGMQ is a real message queue on Postgres (visibility timeout, delay, archive/delete, etc.) with a Python SDK, and there's no broker for it yet.

Describe the solution you'd like

A taskiq broker backed by PGMQ, similar to the other broker packages.

Happy to help implement it.

• PGMQ: https://github.com/pgmq/pgmq
• Python SDK: https://github.com/pgmq/pgmq-py

Describe alternatives you've considered

No response

Which component would this affect?

Broker