web-users: make sure http starts on mariadb upgrades

After the change is deployed verify the resulting units are enabled.

roles/web-users/files/docker-web-users-http.systemd

@@ -2,3 +2,8 @@
 # (the unix socket changes)
 [Unit]
 PartOf=mariadb@users.service
+
+# Make sure 'systemctl start mariadb@users' also brings up this unit. For
+# example during mariadb package upgrades.
+[Install]
+WantedBy=mariadb@users.service