CI: add workflow to also build tagged docker images

.github/workflows/docker.yml

-name: ci
+name: Dockerhub
 
 on:
   push:
+    tags:
+    - 'i2p-*.*.*'
+    branches:
+    - master
 
 jobs:
   docker:
     runs-on: ubuntu-latest
     steps:
-      -
-        name: Set up QEMU
+      - name: Set up QEMU
         uses: docker/setup-qemu-action@v3
-      -
-        name: Set up Docker Buildx
+      - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
-      -
-        name: Login to Docker Hub
+      - name: Login to Docker Hub
         uses: docker/login-action@v3
         with:
           username: ${{ secrets.DOCKERHUB_USERNAME }}
           password: ${{ secrets.DOCKERHUB_TOKEN }}
-      -
-        name: Build and push
+      - name: Set env
+        run:
+          apt-get install -y sed
+          echo "RELEASE_VERSION=${GITHUB_REF#refs/*/}" | sed 's|master|latest|g' >> $GITHUB_ENV
+      - name: Build and push
         uses: docker/build-push-action@v6
         with:
           push: true
-          tags: geti2p/i2p:latest
+          tags: geti2p/i2p:${{ env.RELEASE_VERSION }}
+      - name: Build and push
+        uses: docker/build-push-action@v6
+        with:
+          push: true
+          tags: geti2p/i2p.i2p:${{ env.RELEASE_VERSION }}