Improve how allen.py takes tag arguments

allen.py (used in running Allen offline) takes tags in the form

--tags=tag1,tag2 or --tags=dd4hep:tag1,tag2|detdesc:tag3,tag4

This MR adds more checks to the given tags as well as allowing tags in the form --tags=dd4hep:tag1,tag2 and --tags=detdesc:tag1,tag2

This stems from the following conversation: !1585 (comment 7929384)