When restoring a dump from a sharded cluster to either a sharded cluster or a replica set, the config collections must be explicitly ignored. This is not clear in the documentation and leads to confusion for customers who wish to convert a sharded cluster to a replica set.

We should instead automatically ignore all config collections in mongodump when reading from a mongos.

After this is done, we'll need to update docs for restoring a sharded cluster and migrating from SC -> RS.