Add :lang yaml module

Removes yaml-mode from :lang data and adds LSP support (#2502).

Closes #2502

Co-authored-by: Seong Yong-ju <sei40kr@gmail.com>

init.example.el

@@ -158,6 +158,7 @@
        ;;swift             ; who asked for emoji variables?
        ;;terra             ; Earth and Moon in alignment for performance.
        ;;web               ; the tubes
+       ;;yaml              ; JSON, but readable
 
        :email
        ;;(mu4e +gmail)