Extension of !237 (merged) based on the assumption that python-debian-team/python-debian!84 (merged) is merged into python-debian/0.1.44. As such, the first commits are just a repeat of !237 (merged).
With this change (on top of !237 (merged)), the RTS parser can replace the existing parser whenever python-debian/0.1.44 is available. The MR based on the assumption that we want to enable the RTS parser automatically in this case. (I have disabled it unconditionally for python-debian/0.1.43 as I deemed it not worth the extra complexity to only support a very limited subset of the formatting options)
I am keeping this as a draft until python-debian-team/python-debian!84 (merged) have been reviewed/merged. However, please feel free to review it already now as it is feature complete once that python-debian MR is merged.