Refactor wallabag stack name and repo variables

Brought in line with other stack naming schemes.

roles/wallabag/tasks/main.yml

@@ -4,7 +4,7 @@
   community.docker.docker_container_exec:
     container: "{{ caddy_container_id }}"
     command: >
-      curl localhost:2019/id/{{ stack.name }}_upstream/
+      curl localhost:2019/id/{{ stack_name }}_upstream/
   register: result
   changed_when: (result.stdout | from_json) != (lookup('template', 'upstream.json.j2') | from_yaml)
   become: true
@@ -12,14 +12,12 @@
 
 - name: Deploy wallabag to swarm
   community.general.docker_stack:
-    name: "{{ stack.name }}"
+    name: "{{ stack_name }}"
     state: present
     prune: yes
     compose:
-      - "{{ stack.compose }}"
-  when: stack is defined
+      - "{{ stack_compose }}"
   become: true
   tags:
     - docker-swarm
   notify: "update wallabag upstream"
-