test: switch to using oauth/sso

Switch the authentication method that the koji builder plugin
uses from mTLS to SSO. Since we are using the mock openid
server from the `osbuild-composer-tests` package. Make this
package a dependency of `koji-osbuild-tests`.

test/container/builder/osbuild-koji.conf

@@ -1,7 +1,11 @@
 [composer]
 server = https://composer/
-ssl_cert = /share/client-crt.pem, /share/client-key.pem
 ssl_verify = /share/client-ca.pem
 
+[composer:oauth]
+client_id = "koji"
+client_secret = "koji"
+token_url = https://composer:8081/token
+
 [koji]
 server = https://localhost:4343/kojihub/