ci: create Docker image on tag

Signed-off-by: Bradley Reynolds <bradley.reynolds@darbia.dev>

Author: shenanigansd

.github/workflows/docker-build-push.yaml

@@ -4,6 +4,8 @@ on:
   push:
     branches:
       - main
+    tags:        
+      - v*
 
 permissions:
   contents: read