[ATMOSPHERE-573] Fix atmosphere_ceph_enabled is not respected in site playbook (#2101)

diff --git a/playbooks/site.yml b/playbooks/site.yml
index d4639ae..e651852 100644
--- a/playbooks/site.yml
+++ b/playbooks/site.yml
@@ -14,6 +14,7 @@
 
 - name: Install Ceph
   import_playbook: vexxhost.atmosphere.ceph
+  when: atmosphere_ceph_enabled | default(true) | bool
 
 - name: Install Kubernetes
   import_playbook: vexxhost.atmosphere.kubernetes