new: [frontend] renamed ``apache`` service to ``frontend``.

The idea here is to separate function and implementor. The service
is ``frontend`` here, and the implementor is ``apache`` charm. It could
change to be ``nginx`` or ``traefik``...

compose.yml

@@ -17,7 +17,7 @@ odoo:
         user: odoo
         dbname: odoo
     web-proxy:
-      apache:
+      frontend:
         domain: mydomain.org
         #server-aliases:
         #  - mydomain2.org
@@ -58,3 +58,5 @@ odoo:
         #     -----END PRIVATE KEY-----
 
 
+frontend:
+  charm: apache