Pick correctionlib files from cvmfs instead of having a copy in our repo

[namapane]

following up discussion in #263 (comment)_

Picking the correction files from cvmfs would have some advantage:

• less AFS load in production (and condor throttling jobs because of that)
• as mentioned by @AlessandroTarabini : "it is quite convenient in case of changes and correction of issues from the POG. At least, we do not have to keep constantly an eye to what is happening in EGM, MUON, and JME, and we always have the most up-to-date corrections."

Disadvantages:

• we do not have control of what is changed; potentially; files could be updated in the middle of a production of ours, without us realizing it (cvmfs is not versioned)

[bonanomi]

"it is quite convenient in case of changes and correction of issues from the POG. At least, we do not have to keep constantly an eye to what is happening in EGM, MUON, and JME, and we always have the most up-to-date corrections."

I am not sure this is 100% correct. If the POGs release files with an updated name and/or location (many times, eg in EGM, the files are under the space of one of the conveners or the main developers) then our code would not work anyway.

[namapane]

I think in such cases conveners should be asked to conform to the conventions and have their corrections committed as soon as they are approved to the CAT repo (https://gitlab.cern.ch/cms-nanoAOD/jsonpog-integration/-/tree/master), which is synced automatically to /cvmfs/cms.cern.ch/rsync/cms-nanoAOD/jsonpog-integration.
The CAT effort to provide a central repository and dissemination mechanisms is a very remarkable one and it can potentially make analyzer's life much more straightforward if everybody does its bit (less ad-hoc cooking to be replicated by everybody...)

[bonanomi]

Yes, I think all the POGs are trying to move in that direction. The muon POG corections have just been released and they are not available centrally yet, but definitely on the long run the plan is to have everything compliant with CAT requests.