Add an additional integration test, which builds a fedora-32 image via
the newly moved composer API.
This adds a new certificate for clients to authenticate, with
CN=client.osbuild.org.
Also stop allowing certificates with `CN=worker.osbuild.org` in the
`osbuild-composer.toml` used in tests and amend `osbuild-auth-tests` to
use `CN=client.osbuild.org` for accessing the koji API.
Heavily based on an earlier version of this test in `test/cmd/aws.sh` by
Sanne Raymaekers.
