patch 9.1.0304: filetype: cgdb config file is not recognized

Problem:  filetype: cgdb config file is not recognized
Solution: Detect cgdbrc files as cgdbrc filetype
          (Wu, Zhenyu)

closes: #14458

Signed-off-by: Wu, Zhenyu <wuzhenyu@ustc.edu>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/ftplugin/cgdbrc.vim

@@ -0,0 +1,21 @@
+" Vim filetype plugin file
+" Language:             cgdbrc
+" Maintainer:           Wu, Zhenyu <wuzhenyu@ustc.edu>
+" Documentation:        https://cgdb.github.io/docs/Configuring-CGDB.html
+" Latest Revision:      2024-04-09
+
+if exists('b:did_ftplugin')
+  finish
+endif
+let b:did_ftplugin = 1
+
+let s:save_cpoptions = &cpoptions
+set cpoptions&vim
+
+let b:undo_ftplugin = 'setl com< cms<'
+
+setlocal commentstring=#%s
+setlocal comments=:#
+
+let &cpoptions = s:save_cpoptions
+unlet s:save_cpoptions