Refactor Joomla role to new docker.* schema

- Move image definition from images.joomla to docker.services.joomla
- Add container name, container_port variable, and healthcheck
- Introduce JOOMLA_IMAGE, JOOMLA_VERSION, JOOMLA_CONTAINER, JOOMLA_VOLUME in vars
- Use volume mapping via docker.volumes.data

See: https://chatgpt.com/share/68af55a9-6514-800f-b6f7-1dc86356936e

roles/web-app-joomla/config/main.yml

@@ -1,5 +1,3 @@
-images:
-  joomla:             "joomla:latest"
 features:
   matomo:             true
   css:                true
@@ -14,3 +12,9 @@ docker:
   services:
     database:
       enabled: true
+    joomla: 
+      image:    joomla
+      version:  latest
+      name:     joomla
+  volumes:
+    data:             "joomla_data"