redhat: forward-port genlog.py updates from c9s

This is forward-port of c9s commit: b9e094da37a1 ("redhat: rewrite genlog and support Y- tags")

It combines various parse functions into a common function that goes over list of tag:regex pairs, which makes parsing and adding new tags simpler. It also updates regexes to be aligned with ones used by webhooks.

This is primarily for future RHEL downstreams, so I kept the script identical to c9s.

Signed-off-by: Jan Stancek jstancek@redhat.com