postgres: Introduce indexes validity check

[abeglu]

No description provided.

[kofrezo]

We have this check already:

$ mon -c postgres_invalid_indexes_eu1_game
postgres_invalid_indexes_eu1_game - OK - All indexes are valid

[abeglu]

Currently, we're creating a separate command for each database, but by using this script, we can check multiple databases with a single command.

[seqizz]

I guess single check is a lot cleaner on monitoring side, so LGTM. But please process this with a formatter like ruff. We should start using f-strings at least at this point.