#24475 Current user now resolved JIT rather than at folder config init

This change relates to the user workspace node in the folder creation setup. Previously, if such a node was present in the folder config, toolkit would try to resolve the current shotgun user in the constructor, meaning that any machine that wanted to carry out folder creation had to have a valid shotgun user associated with each machine account. This was causing problems with setups that had a special machine dedicated to do folder creation - this machine needed to be set up with a shogun user account despite not actually creating any user workspaces. This change moves the resolve to happen JIT, meaning that it is only when you *actually* try to create a user workspace that the current user is resolved.