update Sherpack name with SCRAM_ARCH and CMSSW_VERSION

[shimashimarin]

PR description:

Add CMSSW_VERSION and SCRAM_ARCH to the Sherpack:

• Now the Sherpack is a single tarball file just like Gridpack for MG5, i.e., sherpa_<process_name>MASTER<SCRAM_ARCH>_<CMSSW_VERSION>.tar.xz. No longer a folder that hard to fix SCRAM_ARCH and CMSSW_VERSION information.
• A script convert_sherpack.sh that helps to convert the existing Sherpack to the new format is provided in the folder GeneratorInterface/SherpaInterface/data/, no need to regenerate Sherpack from scratch. A ReadME.md is also offered in the same folder to guide users to convert the Sherpack with one line command.
• GeneratorInterface/SherpaInterface/src/SherpackFetcher.cc also updated accordingly.

PR validation:

• Local test passed. Workflow doesn't changed as GEN documentation: Set CMSSW environment -> run ./MakeSherpaLibs.sh to get libraries -> run ./PrepareSherpaLibs.sh to generate sherpack -> cmsDriver.py to get event-generation script.
• Also test of using existing Sherpack with convert_sherpack.sh. It works properly.

[cmsbuild]

cms-bot internal usage

[cmsbuild]

+code-checks

Logs: https://cmssdt.cern.ch/SDT/code-checks/cms-sw-PR-50955/49365

[cmsbuild]

A new Pull Request was created by @shimashimarin for master.

It involves the following packages:

• GeneratorInterface/SherpaInterface (generators)

@cmsbuild, @lviliani, @mkirsano, @sensrcn, @theofil can you please review it and eventually sign? Thanks.
@alberto-sanchez, @mkirsano, @thuer this is something you requested to watch as well.
@ftenchini, @mandrenguyen, @sextonkennedy you are the release manager for this.

cms-bot commands are listed here