Allow GH Actions to build docker images for linux/arm64

Allow Github Actions to also build docker images for linux/arm64 and
adapted workflow to be able to use the multi-stage Dockerfile.

.github/workflows/github_release_docker.yml

@@ -7,44 +7,21 @@ on:
   workflow_dispatch:
 
 jobs:
-  rust_build:
-    name: Build Nimiq with release flag
-    runs-on: ubuntu-22.04
-    steps:
-      - uses: actions/checkout@v4
-      - uses: dtolnay/rust-toolchain@stable
-      - name: Build binaries in release mode
-        run: |
-          cargo build --release
-      - name: Archive production artifacts
-        uses: actions/upload-artifact@v4
-        with:
-          name: nimiq-dist
-          path: |
-            target/release/nimiq-client
-            target/release/nimiq-bls
-            target/release/nimiq-address
-            target/release/nimiq-rpc
-
   build_docker:
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-24.04
     name: Build & publish docker image
-    needs: rust_build
+    strategy:
+      fail-fast: false
+      matrix:
+        platform:
+          - linux/amd64
+          - linux/arm64
+
     steps:
       - name: Check out the repo
         uses: actions/checkout@v4
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
-      - name: Download nimiq client artifact from previous job
-        uses: actions/download-artifact@v4
-        with:
-          name: nimiq-dist
-          path: target/release/
-
-      - name: Run some commands
-        run: |
-          ls target/release/ -al
-          chmod -R +x target/release/
       - name: Docker meta
         id: meta
         uses: docker/metadata-action@v5
@@ -61,6 +38,7 @@ jobs:
           password: ${{ secrets.GITHUB_TOKEN }}
 
       - name: Build and push
+        id: build
         uses: docker/build-push-action@48aba3b46d1b1fec4febb7c5d0c644b249a11355
         with:
           context: .
@@ -76,3 +54,17 @@ jobs:
           labels: ${{ steps.meta.outputs.labels }}
           cache-from: type=gha
           cache-to: type=gha
+          platforms: ${{ matrix.platform }}
+
+      - name: Export digest
+        run: |
+          mkdir -p ${{ runner.temp }}/digests
+          digest="${{ steps.build.outputs.digest }}"
+          touch "${{ runner.temp }}/digests/${digest#sha256:}"          
+
+      - name: Upload digest
+        uses: actions/upload-artifact@v4
+        with:
+          name: digests-${{ env.PLATFORM_PAIR }}
+          path: ${{ runner.temp }}/digests/*
+          if-no-files-found: error