test/cmd: add api.sh

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.

cmd/osbuild-auth-tests/main_test.go

@@ -181,7 +181,7 @@ func TestKojiAPIAuth(t *testing.T) {
 			subj     string
 			success  bool
 		}{
-			{"valid CN 1", "/CN=worker.osbuild.org", true},
+			{"valid CN 1", "/CN=client.osbuild.org", true},
 			{"valid CN 2", "/CN=localhost", true},
 			{"invalid CN", "/CN=example.com", false},
 		}