During the implementation of query stats for count and distinct, we found that the CoundCmd has a resolved NamespaceString in the execution path by the time we register the request for query stats. 

When comparing to other commands such as Find and Agg, it looks like:

• AggCmdShape only allows a NamespaceString in its constructor.
• CountCmd always resolves the NamespaceString.
• FindCmd also seems to resolve any uuid to a NamespaceStri before we register the request.

This seems to indicate that we always have a resolved NamespaceString by the time we want to register the request for query stats. In particular, AggCmdShape does not allow a NamespaceStringOrUUID in its constructor, only a NamespaceString. 

As part of this ticket, we should verify if all use cases for query stats provide a NamespaceString at the time of request registration, and if so, we should change the interfaces and the type of the member query_shape::Shape::nssOrUUID to be a NamespaceString. We should only accommodate the UUID case if there is a need to do so.