Add more PostgreSQL settings

This adds Omnibus support (and sensible defaults) for the following PostgreSQL settings:

• effective_io_concurrency
• max_worker_processes
• max_parallel_workers_per_gather
• log_lock_waits
• deadlock_timeout
• track_io_timing

See the following issues for more information:

• https://gitlab.com/gitlab-com/infrastructure/issues/1556
• https://gitlab.com/gitlab-com/infrastructure/issues/1352
• https://gitlab.com/gitlab-com/infrastructure/issues/1351