feat: provide option to disable CSV log table

[stackane]

The current code implies the csvlog option to be used (see post_init.sh).

However, other than the special case handled in maybe_pg_upgrade.py (which could perfectly work fine with any other file-based log format PostgreSQL currently offers, except stderr), I cannot see any use of the explicitly created public.postgres_log table.

Nevertheless, if for some reason the CSV log gets really big, the vacuumdb as executed in on_role_change.sh or pg_upgrade.py can easily result into a smaller instance (in terms of memory limits) end up in an OOM-killed loop (resulting in a CrashLoopBackoff in Kubernetes).

Unless I am missing something fundamental, this should not cause any harm.