Only build the AAB, since it's all we're uploading. Earlier the apk was
still useful as I was downloading it for manual testing, but now all
testing is done by downloading the release from the app store in a
Closed Testing List.
Now whenever we run 'flutter run' or 'flutter build' we need to pass the
flavour flag. It seems there is no way to set a default flavour.
This is required as I want to be able to not have to reconfigure my
local GitJournal app (which I use for note-taking) vs the one I'm
developing where I might change many different settings for the basis of
testing.
Specially since I don't use Github/GitLab to store my notes, so the
setup process is a bit more involved.
