Add new GitLab CI/CD predefined environment variables: CI_COMMIT_AUTHOR
### Release notes
Previously, if you wanted to know the author of a commit, you would need to retrieve this with an extra API call. Now this details is readily available as predefined CI/CD variables by using `CI_COMMIT_AUTHOR`.
Thanks to [Craig Andrews](https://gitlab.com/candrews) for this contribution!
https://docs.gitlab.com/ee/ci/variables/predefined_variables.html
### Proposal
The variable CI_COMMIT_AUTHOR seems to be missing in the predefined variables.
The only way to get the author of a commit is to do an extra API call.
Is there any problem to include it in the predefined variable ?
Reference: https://docs.gitlab.com/ee/ci/variables/predefined_variables.html
issue