The current public API of FilteringMetadataCache only exposes the same free functions found in the shard_filtering_metadata_refresh.cpp file, along with some additional necessary functions that access the ShardServerCatalogCacheLoader. We can consider what we want to expose in the public API and possibly refine some methods.

The goal of this ticket is to remove the `waitFor.*Flush` methods from the FilteringMetadataCache. The implementer should decide if it has to be a parameter of the refresh or if the wait should always be implicit.