r/postgresql-server: Add script to upgrade database

The `postgresql-upgrade.sh` script arranges to run `pg_upgrade` after a
major PostgreSQL version update.  It's scheduled by a systemd unit,
_postgresql-upgrade.service_, which runs only after an OS update.

roles/postgresql-server/tasks/main.yml

@@ -1,6 +1,8 @@
 - name: ensure postgresql-server is installed
   package:
-    name: postgresql-server
+    name:
+    - postgresql-server
+    - postgresql-upgrade
     state: present
   tags:
   - install
@@ -130,6 +132,35 @@
   tags:
   - systemd
 
+- name: ensure postgresql-upgrade script is installed
+  copy:
+    src: postgresql-upgrade.sh
+    dest: /usr/local/libexec/postgresql-upgrade
+    owner: root
+    group: root
+    mode: u=rwx,go=rx
+  tags:
+  - postgresql-upgrade
+- name: ensure postgresql-upgrade systemd unit is installed
+  copy:
+    src: postgresql-upgrade.service
+    dest: /etc/systemd/system/postgresql-upgrade.service
+    owner: root
+    group: root
+    mode: u=rw,go=r
+  notify:
+  - reload systemd
+  tags:
+  - postgresql-upgrade
+  - systemd
+
+- name: ensure postgresql-upgrade service starts when needed
+  service:
+    name: postgresql-upgrade
+    enabled: true
+  tags:
+  - postgresql-upgrade
+  - service
 - name: ensure postgresql starts at boot
   service:
     name: postgresql