Enable per-database control of postgres logging

[acozine]

User story

As a developer or operations engineer, I sometimes want to enable verbose logging for a single database within our postgresql environment. I'd like to be able to run a playbook to switch the logging level for individual databases, with a variable in this repo as a source of truth.

Follow-up to #5257 (comment).

Acceptance criteria

• I can update a variable in group_vars, run a playbook, and change the log level for a single postgresql database.
• it would be great if the playbook also returned the current setting for each database

Concrete example

During testing or troubleshooting, I might want all statements logged. During regular runtime, I want minimal logging.

Implementation notes, if any

The command to change per-database logging manually is:

ALTER DATABASE your_database_name
SET log_statement = 'all';

See this ServerFault question.
Other possibly helpful resources:
BetterStack blog post
PostgreSQL docs