Add codeowners to double check the version update

Related to gitlab-org/gitlab#322930 (closed)

This change adds CODEOWNERS file to prevent major version of analyzer from being updated unnoticed and adopts suggestions from https://about.gitlab.com/handbook/engineering/development/secure/release_process.html#security-fixes-of-go to Ruby Dockerfile.

Once merged, we can enable MR approvals rules: https://docs.gitlab.com/ee/user/project/merge_requests/approvals/rules.html#code-owners-as-eligible-approvers