gitlab-ci: check gradle checksums against official list
This adds a CI job to do two things:
- check the gradle checksums in makebuildserver against what it published on https://gradle.org/release-checksums/
- check whether newer versions of gradle are available versus what is listed in makebuilderver. Here's an example: https://gitlab.com/eighthave/fdroidserver/-/jobs/290736325
Edited by Hans-Christoph Steiner