Add support for Unsorted List about diffsync

[glennmatthews]

Can we just use set instead of list in this case, or is there a case where we want to preserve the order within the adapter and just ignore order when diffing?

[itdependsnetworks]

Speaking a bit out of school here, but I do think we want to keep order, but sometimes diff unordered

[glennmatthews]

That makes sense. This should be relatively simple to do within the scope of the existing DSyncModelFlags paradigm if we want this to be toggle at a per-model level; if we need it to be configurable at a per-field level (e.g. Site.devices should be sorted while Site.vlans should be unsorted) then that will of course be more complex to implement.