Add codeowners file with team OIS maintainers.

See: 
https://help.github.com/en/github/creating-cloning-and-archiving-repositories/about-code-owners

.github/CODEOWNERS

@@ -0,0 +1,7 @@
+# Each line is a file pattern followed by one or more owners.
+
+# These owners will be the default owners for everything in
+# the repo. Unless a later match takes precedence,
+# these owners will be requested for review when someone
+# opens a pull request.
+*       @dav3r @felddy @jsf9k @mcdonnnj