Add play to everything playb. for deploying Docker Compose applications

Also introduce a new group for hosts, for which this play should be run,
called Docker_Compose_Hosts.
Finally add cit-ansible-test and cit-docker-host to this group with an
empty project list initially.

inventories/hetzner/host_vars/cit-ansible-test.yaml

@@ -0,0 +1 @@
+docker_compose__projects: [ ]

inventories/hetzner/host_vars/cit-docker-host.yaml

@@ -0,0 +1 @@
+docker_compose__projects: [ ]

inventories/hetzner/hosts.yaml

@@ -19,3 +19,7 @@ all:
       hosts:
         cit-ansible-test:
         cit-docker-host:
+    Docker_Compose_Hosts:
+      hosts:
+        cit-ansible-test:
+        cit-docker-host: