While there, include integration testing to make sure the script
is working as intended before using it.
While there, edit maketarball.bash's comments.
This diff modifies all the github actions that produce assets to
publish on a release called rolling when we are not building a tag.
If everything goes as planned, we should be able to provide
people with automatically generated fresh binaries for testing.
While there, introduce caching for all builds to make them
as fast as possible. I suspect gomobile based builds will not
see any speed up but other builds most likely will.
See https://github.com/ooni/probe/issues/2249
