CODEOWNERS: Set @JuliaLang/committers-available-to-review as the global (default) codeowners for the JuliaLang/julia repo (#58315)

Author: DilumAluthge

.github/CODEOWNERS

@@ -1,3 +1,13 @@
+# This is a comment.
+# 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,
+# a member of the `@JuliaLang/committers-available-to-review` team
+# will be requested for review when someone opens a pull request.
+*       @JuliaLang/committers-available-to-review
+
 CODEOWNERS @JuliaLang/github-actions
 /.github/ @JuliaLang/github-actions
 /.buildkite/ @JuliaLang/github-actions