caddy-frontend: Extend caucase stack and install it

software/caddy-frontend/common.cfg

@@ -12,6 +12,7 @@ extends =
   ../../component/6tunnel/buildout.cfg
 
   ../../stack/nodejs.cfg
+  ../../stack/caucase/buildout.cfg
 # Monitoring stack (keep on bottom)
   ../../stack/monitor/buildout.cfg
 
@@ -63,6 +64,7 @@ eggs =
 eggs +=
   websockify
   erp5.util
+  ${caucase-eggs:eggs}
 
 [template-common]
 recipe = slapos.recipe.template:jinja2