Allow not managing table settings

[reidmv]

This is to provide for situations, like in the PE Extra Large
architecture, where the PuppetDB database does not exist on the
PostgreSQL system being tuned. In PE XL, the master and the master
replica run a PostgreSQL system for all databases except for PuppetDB.

[npwalker]

Technically this can already be achieved by setting the parameters on table_settings to false or undef as appropriate.

The only thing I'm contemplating is if manage_postgresql_settings false should be the thing that causes table_settings to not be included. I think it's a logical error that there's no way to avoid that in the present case.

[reidmv]

@npwalker ok. Let me know what conclusion you arrive at on what should be done. I'm happy to make changes or close this PR based on your decision.