refactor: use variables for graylog stack image versions

Move hardcoded image versions to variables defined in main.yml for
easier version management in one place.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

ansible/roles/podman/tasks/containers/debyltech/graylog.yml

@@ -75,7 +75,7 @@
 - import_tasks: podman/podman-check.yml
   vars:
     container_name: graylog-mongo
-    container_image: docker.io/mongo:6
+    container_image: "{{ mongo_image }}"
   tags: graylog
 
 - name: create graylog-mongo container
@@ -83,7 +83,7 @@
   become_user: "{{ podman_user }}"
   containers.podman.podman_container:
     name: graylog-mongo
-    image: docker.io/mongo:6
+    image: "{{ mongo_image }}"
     state: started
     restart_policy: on-failure:3
     log_driver: journald
@@ -103,7 +103,7 @@
 - import_tasks: podman/podman-check.yml
   vars:
     container_name: graylog-opensearch
-    container_image: docker.io/opensearchproject/opensearch:2
+    container_image: "{{ opensearch_image }}"
   tags: graylog
 
 - name: create graylog-opensearch container
@@ -111,7 +111,7 @@
   become_user: "{{ podman_user }}"
   containers.podman.podman_container:
     name: graylog-opensearch
-    image: docker.io/opensearchproject/opensearch:2
+    image: "{{ opensearch_image }}"
     state: started
     restart_policy: on-failure:3
     log_driver: journald
@@ -135,7 +135,7 @@
 - import_tasks: podman/podman-check.yml
   vars:
     container_name: graylog
-    container_image: docker.io/graylog/graylog:6.0
+    container_image: "{{ image }}"
   tags: graylog
 
 # Graylog uses host network to reach MongoDB/OpenSearch on 127.0.0.1
@@ -145,7 +145,7 @@
   become_user: "{{ podman_user }}"
   containers.podman.podman_container:
     name: graylog
-    image: docker.io/graylog/graylog:6.0
+    image: "{{ image }}"
     state: started
     restart_policy: on-failure:3
     log_driver: journald