Surface certain messages at the end of playbook execution

Fixes #106 (Github Issue).

roles/matrix-common-after/tasks/dump_runtime_results.yml

@@ -0,0 +1,6 @@
+# Ansible outputs the message in the `item=` field.
+# It's unnecessary to output it again in the actual message, so we don't.
+- debug:
+    msg: ""
+  with_items: "{{ matrix_playbook_runtime_results }}"
+  when: "matrix_playbook_runtime_results is defined and matrix_playbook_runtime_results|length > 0"

roles/matrix-common-after/tasks/main.yml

@@ -7,3 +7,7 @@
   when: run_stop|bool
   tags:
     - stop
+
+- import_tasks: "{{ role_path }}/tasks/dump_runtime_results.yml"
+  tags:
+    - always

roles/matrix-postgres/tasks/setup_postgres.yml

@@ -18,9 +18,16 @@
     matrix_postgres_docker_image_to_use: "{{ matrix_postgres_docker_image_latest if matrix_postgres_detected_version_corresponding_docker_image == '' else matrix_postgres_detected_version_corresponding_docker_image }}"
   when: matrix_postgres_enabled|bool
 
-- name: Warn if on an old version of Postgres
-  debug:
-    msg: "NOTE: Your setup is on an old Postgres version ({{ matrix_postgres_docker_image_to_use }}), while {{ matrix_postgres_docker_image_latest }} is supported. You can upgrade using --tags=upgrade-postgres"
+- name: Inject warning if on an old version of Postgres
+  set_fact:
+    matrix_playbook_runtime_results: |
+      {{
+        matrix_playbook_runtime_results|default([])
+        +
+        [
+          "NOTE: Your setup is on an old Postgres version ({{ matrix_postgres_docker_image_to_use }}), while {{ matrix_postgres_docker_image_latest }} is supported. You can upgrade using --tags=upgrade-postgres"
+        ]
+      }}
   when: "matrix_postgres_enabled|bool and matrix_postgres_docker_image_to_use != matrix_postgres_docker_image_latest"
 
 # Even if we don't run the internal server, we still need this for running the CLI