Now that all interaciton with the koji API happens in the workers
we can drop koji configuration from composer itself. This means
that composer no longer needs to be provisioned with kerberos
credentials, and does not need to know about which koji servers
the workers support.
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.
