Add python script for GitLab releases.
The main purpose of the script is to create a SIESTA release on GitLab.
The script may also be used to delete a release from GitLab or to replace the description (text) of an existing release. These two additional features will work for any GitLab release (not only for SIESTA releases).
An earlier version of this script was used to release SIESTA 4.1.5 (and later it was used to modify the 4.1.5 release description).