vim-patch:9.1.0778: filetype: lf config files are not recognized

Problem:  filetype: lf config files are not recognized
Solution: detect lfrc files as lf filetype, include a syntax
          script for lf files (Andis Spriņķis).

References:
- https://github.com/gokcehan/lf

closes: vim/vim#15859

0f146b7925

Co-authored-by: Andis Spriņķis <spr.andis@protonmail.com>

runtime/lua/vim/filetype.lua

@@ -1611,6 +1611,7 @@ local filename = {
   ['ldaprc'] = 'ldapconf',
   ['.ldaprc'] = 'ldapconf',
   ['ldap.conf'] = 'ldapconf',
+  ['lfrc'] = 'lf',
   ['lftp.conf'] = 'lftp',
   ['.lftprc'] = 'lftp',
   ['/.libao'] = 'libao',