config: Remove DB metrics configuration

Scraping DB metrics requires expensive queries to the Praefect DB. By default these metrics are split out to its own independent endpoint for scraping. This reduces resouce consumption by enabling separate configuration of the metrics scraping intervals. Currently the prometheus_exclude_database_from_default_metrics configuration exists to toggle this behavior. It is now desired for the default behavior to be the only option. This change removes the configuration option and makes it so DB metrics cannot be combined with other metrics on the same endpoint.

Closes: #3996 (closed)