koji: Add playbooks for Koji

The `koji.yml` playbook can be used to deploy an entire Koji ecosystem.
It is composed of three smaller playbooks:

* `koji-hub.yml`: Deploys the Koji hub, GC, and Kojira
* `koji-web.yml`: Deploys the Koji Web GUI
* `koji-builder.yml`: Deploys the Koji builder

koji.yml

@@ -0,0 +1,8 @@
+- import_playbook: koji-hub.yml
+- import_playbook: koji-web.yml
+# For new installations, it is not safe to start kojid immediately, as the
+# `koji add-host` command needs to be run first to avoid the "User n is not a
+# host" error. Until a `koji_user` module exists to automatically handle this,
+# it is best to simply let the user handle it and explicitly apply the
+# `koji-builder.yml` platbook later
+#- import_playbook: koji-builder.yml