ci: Add GitHub Actions workflow for test suite

ci: Add GitHub Actions workflow for test suite

This runs the test suite in various distros. The intention is to use
this to replace the Travis CI setup since it often has rate limit
failures.

Each configuration in the matrix runs in a Docker container, installs
system dependencies and then builds and tests ostree. The scripts are
basically copy and paste of the travis ones with some of the lesser used
features pruned out.

Some differences from the travis setup:

* OS details are gathered from `/etc/os-release` instead of being passed
  in as environment variables.

* The scripts always assume the user is root and don't try to use
  `sudo`.

* The `installcheck` test has been removed since ostree doesn't actually
  use that. It could be added to run the installed tests or
  `gnome-desktop-testing-runner` could just be called directly.

There should be enough flexibility to run other distros like Fedora,
Arch or Alpine. Another option would be to use the other build scripts
in ci/.