Customise CD triggers

- CD can be triggered manually, or automatically whenever a new tag is pushed
- Changes to configuration also trigger an automatic CD run

Re ECFLOW-1967

.github/workflows/cd.yml

@@ -1,11 +1,18 @@
 name: cd
 
 on:
-  push: ~
-
   # Trigger the workflow manually
   workflow_dispatch: ~
 
+  push:
+    # Trigger the workflow when new tags are pushed
+    tags:
+      - '**'
+    # Trigger the workflow when the CD workflow/configuration is updated
+    paths:
+      - .github/cd-*.yml
+      - .github/workflows/cd.yml
+
 jobs:
   deploy-server:
     uses: ecmwf-actions/reusable-workflows/.github/workflows/create-package.yml@v2