add tag prefix for docker images

docker/action.yml

@@ -28,6 +28,9 @@ inputs:
   TAG_LATEST:
     description: "Also tag and push the image as latest"
     default: "false"
+  TAG_PREFIX:
+    description: "Optional prefix to prepend to IMAGE_TAG (e.g. 'dev' produces 'dev-<tag>'). Does not affect the latest tag."
+    default: ""
   WORKING_DIRECTORY:
     description: "Working directory for the Docker build"
     default: "."
@@ -51,7 +54,11 @@ runs:
     - name: Docker Build and Push
       shell: sh
       run: |
-        TAGS="-t ${{ inputs.IMAGE_PATH }}:${{ inputs.IMAGE_TAG }}"
+        TAG="${{ inputs.IMAGE_TAG }}"
+        if [ -n "${{ inputs.TAG_PREFIX }}" ]; then
+          TAG="${{ inputs.TAG_PREFIX }}-${TAG}"
+        fi
+        TAGS="-t ${{ inputs.IMAGE_PATH }}:${TAG}"
         if [ "${{ inputs.TAG_LATEST }}" = "true" ]; then
           TAGS="$TAGS -t ${{ inputs.IMAGE_PATH }}:latest"
         fi