CI: Multiarch Docker toolchain (#641)

Co-authored-by: あく <alleteam@gmail.com>

.github/workflows/build_toolchain.yml

@@ -0,0 +1,46 @@
+name: 'Build toolchain Docker image'
+
+on:
+  push:
+    branches:
+      - dev
+    tags:
+      - '*'
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+      - name: Docker meta
+        id: meta
+        uses: docker/metadata-action@v3
+        with:
+          images: flipperdevices/flipperzero-toolchain
+          flavor: latest=${{ startsWith(github.ref, 'refs/tags/') && !endsWith(github.ref, 'rc')}}
+          tags: |
+            type=ref,event=branch
+            type=ref,event=tag
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v1
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+      - name: Login to DockerHub
+        uses: docker/login-action@v1
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+      - name: Build and push
+        id: docker_build
+        uses: docker/build-push-action@v2
+        with:
+          context: docker/
+          push: true
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+          platforms: linux/amd64,linux/arm64
+          cache-from: type=registry,ref=flipperdevices/flipperzero-toolchain:buildcache
+          cache-to: type=registry,ref=flipperdevices/flipperzero-toolchain:buildcache,mode=max