Add auto-deploy support to manage_version.rb

This MR introduces a new CI job

This new job will only run if $TRIGGER_JOB is set to tag_auto_deploy.

It will execute scripts/tag_auto_deploy.rb that will take care of the following steps:

1. Configure git client in order to push new commits
2. Invoke scripts/manage_version.rb
3. Commit the changes
4. Tag the commit
5. Push both the current branch and the new tag

This also introduces a new --auto-deploy options for scripts/manage_versions.rb that will take care of updating version for an auto-deploy build.

Changes on an auto-deploy build:

• chart-version cannot be specified, it has the same value of app-version
• version fetcher relies on environment variables for components versions
• version_mapping is not updated

Related to gitlab-com/gl-infra/delivery#697 (closed)