flatpak-builder: add support for D-Bus tests
If the run-test input is true, automatically start a session bus and add
DBUS_SESSION_BUS_ADDRESS environment variable when modifying the manifest.
fixes #25
This is not terribly elegant, but I didn't want to refactor a bunch of the code flow and make it too difficult to review. I believe all the potential exceptions are caught, though.
it looks pretty good to me! before getting this one merged, I would like to tackle #60 as the repo was moved to the Flatpak repo and we would like to keep only the base image here and have the runtime ones produced by Flathub itself along with something like flathub-publish
The codespell check seems not to be correct nor related to this PR, so we can merge it and figure out what to do with Codespell after.