SubDocument error statuses are defined on ResponseStatus

See also: NCBC-2831

Status like ResponseStatus.SubDocPathInvalid are actually returned in the body of a SubDocument error response, not the top-level status.

This leads to them being possibly thrown in ResponseStatusExtensions.CreateException, but that's probably unreachable code as they will never actually be encountered at that level.

We should check the protocol and be absolutely sure what the server could possibly return, then move those SubDocument error statuses to a separate enum and put the handling/throwing of those exceptions under a different method.