feat: added disabled_when config option

[Poulbi]

Enables to create your own custom conditions by executing a function if it is present in the table. The function should return true when the pair is disabled and nil or false when not.

I made this so that I could disable certain pairs when in comments with this snippet:

local function in_comment()
	if
		require("cmp.config.context").in_treesitter_capture("comment") == true
		or require("cmp.config.context").in_syntax_group("Comment")
	then
		return true
	else
		return false
	end
end