feat(workflow) add GA Workflow for SuperNode Docker image (#3285)

- Adds a new GitHub Action Workflow for building SuperNode Docker images.
- Removes the old Client image Workflow.

Signed-off-by: Robert Steiner <robert@flower.ai>

.github/workflows/docker-supernode.yml

@@ -0,0 +1,52 @@
+name: Build docker SuperNode image
+
+on:
+  workflow_dispatch:
+    inputs:
+      flwr-version:
+        description: "Version of Flower."
+        required: true
+        type: string
+
+permissions:
+  contents: read
+
+jobs:
+  build-supernode-images:
+    name: Build images
+    uses: ./.github/workflows/_docker-build.yml
+    # run only on default branch when using it with workflow_dispatch
+    if: github.ref_name == github.event.repository.default_branch
+    strategy:
+      fail-fast: false
+      matrix:
+        image: [
+          {
+            py-version: "3.8",
+            tags: "${{ github.event.inputs.flwr-version }}-py3.8-ubuntu22.04"
+          },
+          {
+            py-version: "3.9",
+            tags: "${{ github.event.inputs.flwr-version }}-py3.9-ubuntu22.04"
+          },
+          {
+            py-version: "3.10",
+            tags: "${{ github.event.inputs.flwr-version }}-py3.10-ubuntu22.04"
+          },
+          {
+            py-version: "3.11",
+            # those are two tags <version>-py3.11-py3.11-ubuntu22.04 and <version> separated by a \n
+            tags: "${{ github.event.inputs.flwr-version }}-py3.11-ubuntu22.04\n${{ github.event.inputs.flwr-version }}"
+          },
+        ]
+    with:
+      namespace-repository: flwr/supernode
+      file-dir: src/docker/supernode
+      build-args: |
+        FLWR_VERSION=${{ github.event.inputs.flwr-version }}
+        PYTHON_VERSION=${{ matrix.image.py-version }}
+        UBUNTU_VERSION=ubuntu22.04
+      tags: ${{ matrix.image.tags }}
+    secrets:
+      dockerhub-user: ${{ secrets.DOCKERHUB_USERNAME }}
+      dockerhub-token: ${{ secrets.DOCKERHUB_TOKEN }}