Always upload releases to CVMFS

[fstagni]

As discussed in DIRACGrid/DIRAC#4604 and in https://indico.cern.ch/event/932018/note/ we should upload automatically all DIRAC releases/tarballs to (also) CVMFS. This can be done by storing proxies and using secrets. This includes DIRACOS and DIRACOS2.

Andrei has a couple scripts putting various DIRAC tarballs in CVMFS. Not yet added on the repository, at the moment they are stand-alone administrator tools.