Add gitlab-ci-clone python script
Gitlab CI does not support dropping it's sources into a subfolder, but we need this eg. in our Craft templates. However a simple git clone command works well for main branches, but not for merge requests with the source branch in a fork. Dealing with such situations is quite complex hence a python script instead of custom coded for the different platforms (powershell, bash,...) makes sense.
This is related to !120 (merged)