feat: enable in-database configuration for pool settings

[laurenceisla]

Closes #3110.

[laurenceisla]

@steve-chavez

Managed to make it reload the pool configurations, but I'm not very familiarized with the process: I'm not sure if it needs to destroy the old pool or where. For example, I have doubts on what would happen here:

postgrest/src/PostgREST/CLI.hs

Lines 40 to 42 in b2095a8

	bracket
	(AppState.init conf)
	AppState.destroy

I'm also not familiarized with the debWorker and if it needs to be updated too.

On a side note, I added a test that checks if the db-pool configuration is reloaded correctly. It fails in the main branch.... although now, the test_no_pool_connection_available is failing...