Recently it was discovered that some clusters could have unexpected documents ( garbage) in config.databases in particular we observed (AF-1692) that customer coming from old versions of mongodb (< 5.0 ) could have an entry in config.databases for the `admin` db even if today is impossible to create this database that is considered internal.

The goal of this ticket is to extend our testing coverage to include this scenario.
One option could be to artifically inject these type of unexpected document in some of our core passthrough suites so that we ensure that normal workflow and functionality will work as expected even in the presence of those unexpected entries in config.databases.