patch 9.1.1764: filetype: CODEOWNERS file not recognized

Problem:  filetype: CODEOWNERS file not recognized
Solution: Detect CODEOWNERS file as codeowners filetype, include a
          syntax and filetype plugin (Jon Parise).

CODEOWNERS files define code ownership rules for GitHub-hosted (and
other) repositories. The syntax is similar to 'gitignore' files but
differs in enough ways to warrant its own filetype.

References:
- https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-code-owners

closes: #18299

Signed-off-by: Jon Parise <jon@indelible.org>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/syntax/testdir/input/codeowners.txt

@@ -0,0 +1,12 @@
+# This is a comment.
+# Each line is a file pattern followed by one or more owners.
+
+*       @global-owner1 @global-owner2
+*.js    @js-owner #This is an inline comment.
+*.go	docs@example.com
+*.txt	@octo-org/octocats
+/a/b/	@doctocat
+docs/*	docs@example.com @other
+**/logs @octocat
+
+# vim: set ft=codeowners: