Resolve "add env var for single-dsid mode skimming"

Release notes

Added an environment variable to force xAODskimming algorithm to run in single-DSID mode (errors if a seocnd DSID is encountered in the same job) and create a fixed output file name (both aspects are needed to run CAF based xAOD skimming on the grid)

Details

Closes #376 (closed)