fix: purge stack to avoid issue with immutable config..

.. wherein stack-ssh-deploy will fail, because Docker swarm configs
can't be changed post-definition, but we're not using any versioning
here to specify new content. So, hoping this should remove the stack
(and configs) and allow things to Just Work™.

.drone.yml

@@ -7,6 +7,7 @@ steps:
     settings:
       stack: recipes_coopcloud_tech_json
       host: mellor.coopcloud.tech
+      purge: true
       deploy_key:
         from_secret: drone_ssh_coopcloud_mellor