chore: add cli team to github codeowners file (aws-amplify#6147)

> You can use a CODEOWNERS file to define individuals or teams that are
> responsible for code in a repository.

This will cause the "Amplify CLI" team to automatically be included to
the "Reviewers" list on all incoming Pull Requests.

Refer: https://docs.github.com/en/free-pro-team@latest/github/creating-cloning-and-archiving-repositories/about-code-owners

.github/CODEOWNERS

@@ -0,0 +1 @@
+*   @aws-amplify/amplify-cli