This removes the osbuild-composer-cloud package, binary, systemd units,
the (unused) test binary, and the (only-run-on-RHEL) test in aws.sh.
Instead, move the cloud API into the main package, using the same
socket as the koji API, osbuild-composer-api.socket. Expose it next to
the koji API on route `/api/composer/v1`.
This is a backwards incompatible change, but only of the -cloud parts,
which have been marked as subject to change.
Add a simple unit test for the koji API.
This adds a Handler() method to the koji.Server struct, which made
writing the test easier. This is a direction we want to go in anyway in
the future.
