feat: register Neorg filetype in plenary.filetype

[kashelkin]

It lets Telescope detect Neorg files and attach Treesitter highlighting to preview buffers.

[max397574]

I'm not sure if we want this because it would be like a duplicate after 0.10 release
edit: nvm I got an idea

[vhyrro]

Hey!

This is a good idea on the surface but Neorg is slowly depending less and less on plenary and I don't fancy making it a hard dependency once again. Unsure why telescope uses a filetype detection system that isn't the native one but a wrapper/extension on top of it 😅.

I think the best course of action is to wait for Neovim 0.10.0 where norg becomes an officially recognized filetype and where more than one filetype hook is not required any longer.

Thank you for the PR but I don't see this being the proper solution :)