[github]: add code owner (sonic-net#242)

add sonic-kernel team as the code owner for this repo

Signed-off-by: Guohan Lu <lguohan@gmail.com>

CODEOWNERS

@@ -0,0 +1,11 @@
+# This is a comment.
+# Each line is a file pattern followed by one or more owners.
+
+# rules are explained here
+# https://docs.github.com/en/github/creating-cloning-and-archiving-repositories/about-code-owners
+
+# These owners will be the default owners for everything in
+# the repo. Unless a later match takes precedence,
+# @user will be requested for review when someone opens
+# a pull request.
+*       @sonic-kernel