Add an option to use full namespaces

[nnra6864]

Currently, Rider automatically unchecks the namespace provider option on the Assets/Scripts directory.
I personally find this fairly annoying because other editors(such as Zed and nvim) don't really have an option for this(at least that I know of).
Therefore, every other editor will use a full namespace, which makes more sense anyways, whilst Rider will complain about it.
Simply adding an option to Unity settings that would make the Scripts directory a namespace provider would be awesome.