vim-patch:9.1.1549: filetype: pkl files are not recognized

Problem:  filetype: pkl files are not recognized
Solution: detect *.pkl files as pkl filetype, include
          a filetype plugin (Riley Bruins)

References:
https://pkl-lang.org/
https://github.com/apple/pkl

closes: vim/vim#17751

d128889b30

Co-authored-by: Riley Bruins <ribru17@hotmail.com>

runtime/lua/vim/filetype.lua

@@ -949,6 +949,7 @@ local extension = {
   pike = 'pike',
   pmod = 'pike',
   rcp = 'pilrc',
+  pkl = 'pkl',
   PL = detect.pl,
   pli = 'pli',
   pl1 = 'pli',