release branch / CI on gpu

create additional stage, that is only performed on branch release. A standard process would be to create a running develop. After succeeded pipeline, merge into release and if all tests passed (including now the also tests running on gpu), merge into master.

UPDATE: Release stage will behave like develop and master stage. Perform test and coverage as usual, but additionally perform tests on gpu system and from scratch (on cpu). All release branches need to be named like release<whateveryouwant> to match /^release.*$/ . Try to follow the naming release_v<newversion> like release_v0.9.0