CI: rework Github build workflows and Dockerfile

.github/workflows/release.yml

@@ -0,0 +1,50 @@
+name: release
+on:
+  release:
+    types: [published]
+    paths:
+      - .github/workflows/release.yml
+      - cmd/**
+      - internal/**
+      - .dockerignore
+      - .golangci.yml
+      - Dockerfile
+      - go.mod
+      - go.sum
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - env:
+          DOCKER_BUILDKIT: "1"
+        run: docker build --target test .
+
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - env:
+          DOCKER_BUILDKIT: "1"
+        run: docker build --target lint .
+
+  docker:
+    runs-on: ubuntu-latest
+    needs: [test, lint]
+    steps:
+      - uses: actions/checkout@v2
+      - uses: docker/setup-buildx-action@v1
+      - name: Dockerhub login
+        run: echo ${{ secrets.DOCKERHUB_PASSWORD }} | docker login -u qmcgaw --password-stdin 2>&1
+      - name: Docker buildx
+        run: |
+          docker buildx build \
+            --platform=linux/amd64,linux/386,linux/arm64,linux/arm/v6,linux/arm/v7 \
+            --build-arg BUILD_DATE=`date -u +"%Y-%m-%dT%H:%M:%SZ"` \
+            --build-arg COMMIT=`git rev-parse --short HEAD` \
+            --build-arg VERSION=${GITHUB_REF##*/} \
+            -t qmcgaw/private-internet-access:${GITHUB_REF##*/} \
+            -t qmcgaw/gluetun:${GITHUB_REF##*/} \
+            --push \
+            .