Modify release-tools to tag CNG for auto-deploy

After we complete prepping the CNG repo for auto-deploy, it'll be time to enable auto-deploy for CNG. Complete the necessary work inside of release tools to enable auto-deploy tags to be sent to https://gitlab.com/gitlab-org/build/CNG.

We'll utilize a tag that does not include the omnibus sha. So our auto-deploy tag would look like the following (decision on this is in #693 (closed) (closed)):

<MAJOR>.<MINOR>.<TIMESTAMP>+<GitLab sha>

We will utilize our existing tag coming from release tools. So an example tag we would see today would take the milestone that we utilize our current tag, such as: 12.9.202002191723+d42c6afcade

This issue can be closed when performing a the tag rake task, also creates the tag inside of the above repo.