Use XDG_CACHE_HOME for defining cache directory for torch, pip and pre-commit

This MR just replaces the various cache variables by a central XDG_CACHE_HOME, that is respected (at least) by pip, pre-commit and torch. Cache paths were updated accordingly preserving the current behaviour.

assigned to @andre.anjos

changed title from [data.gitlab-ci] Use XDG_CACHE_HOME for defining cache directory for torch, pip and pre-commit to Use XDG_CACHE_HOME for defining cache directory for torch, pip and pre-commit

changed the description

enabled an automatic merge when the pipeline for 6ea51e2c succeeds

merged

mentioned in commit 7fcdb504