[Feature Request] Allow Database filtering for DBM in Postgres integration

[fat0]

As of right now, when using Datadog to monitor Aurora Postgres databases, and when dbm is enabled, the only way to limit the number of databases being monitored is through the ignore_databases option. We have a use case where we have thousands of databases on our Aurora Postgres clusters, and we want to monitor a small subset (as per ticket #1791678). Datadog support suggested creating a feature request for an include_databases option, which would allow for a more targeted approach in selecting the databases from which to collect DBM data.