In C2C replication, we would like to only replicate majority committed data so that we can avoid handling rollbacks of the source cluster. This is now done by using majority readConcern in collection scans in the cloning phase. However, listDatabases/listCollections/listIndexes don't support reading majority committed catalog as the catalog is not versioned. This makes it very hard for an external process to detect when the result returned by these list commands rolls back. This work is to support majority read for listCollections by reading from a majority committed snapshot of the _mdb_catalog without actually introducing versioned catalog.

And it should also work with sharded clusters.