This lets us add tests that trigger in response to dist-git commits.
I originally wrote this with a single message_type for all namespaces,
but then found that I didn't have a way in the trigger rules to specify
that a test (like modlint) should be run on all module dist-git
commits but not on all rpm dist-git commits. To fix this, I created
three separate message types, one for each of the namespaces we
currently have.
This of course means that we can write taskotron checks that check our
taskotron checks.