hacking changelog-d to support not just github but also forgejo and
gerrit is a lot more complicated than it's worth, even moreso since
the entire thing can just as well be done with ~60 lines of python.
this new script is also much cheaper to instantiate (being python),
so having it enabled in all shells is far less of a hassle.
we've also adjusted existing release notes that referenced a gerrit
cl to auto-link to the cl in question, making the diff a bit bigger
closes lix-project/lix#176
Change-Id: I8ba7dd0070aad9ba4474401731215fcf5d9d2130
