improve Docker CI/CD to exit if an image already exists for the current version

.github/workflows/docker.yml

@@ -1,9 +1,6 @@
 name: Docker
 
 on:
-  #  push:
-  #    tags:
-  #      - 'v[0-9]+.[0-9]+.[0-9]+'
   workflow_dispatch:
 
 jobs:
@@ -21,6 +18,13 @@ jobs:
           echo "VERSION=$VERSION" >> $GITHUB_ENV
           echo "version=$VERSION" >> $GITHUB_OUTPUT
 
+      - name: Check there is no existing image with the same version
+        run: |
+          if docker manifest inspect ghcr.io/gyulyvgc/sniffnet:${{ env.VERSION }}; then
+            echo "Image with version ${{ env.VERSION }} already exists"
+            exit 1
+          fi
+
       - name: Set up QEMU
         uses: docker/setup-qemu-action@v3
 
@@ -43,4 +47,3 @@ jobs:
           tags: |
             ghcr.io/gyulyvgc/sniffnet:latest
             ghcr.io/gyulyvgc/sniffnet:${{ env.VERSION }}
-#            ghcr.io/gyulyvgc/sniffnet:${{ github.ref_name }}