Add version update script to CNG to update variables.yml file in during releases
Related to #942 (closed)
With #942 (closed), we are depending on git tags for releases of CNG images. Earlier, necessary variables were passed from
gitlab-(ce|ee) project to CNG via trigger variables. This included
GITLAB_SHELL_VERSION variables, which decides the version of different components should be downloaded. Now we don't have that information anymore in the pipeline, we need a version update script which sets these values in variables.yml file as part of release process, before creating a git tag.
This can be similar to the manage_version script in charts repo, and will be called by release-tools during release.