Draft: Update gitlab CI image and install-xfitter
- Update gitlab CI image to run tests in a standard ROOT docker image (6.26.10-fedora36)
- move to LCG views for installation using cvmfs compiler
- fix
tools/install-xfitter
if curl is used to download packages (was broken so far) - allow to use curl also to download PDFs in
tools/download-lhapdf.sh
- remove references to unused mela package in install-xfitter
- avoid using the cvmfs gcc installation if we are running in the CI
- update apfelxx to 4.7.0
- skip broken apfelgrid installation (needs fixing upstream)
- other minor cleanups