First pass at implementing GitHub actions

This will allow new NGINX unprivileged Docker images to be built and pushed within GitHub actions

Author: alessfg

.github/workflows/build.yml

@@ -0,0 +1,33 @@
+---
+name: build
+"on":
+  workflow_dispatch:
+jobs:
+  docker:
+    name: Build Alpine Stable NGINX Docker image
+    runs-on: ubuntu-20.04
+    steps:
+      - name: Check out the codebase
+        uses: actions/checkout@v3
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v1
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+      - name: Login to Docker Hub
+        uses: docker/login-action@v1
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+      - name: Parse NGINX version
+        id: version
+        run: |
+          echo "::set-output name=major::$(cat stable/alpine/Dockerfile | awk '$1 == "ENV" && $2 == "NGINX_VERSION" { print $3 }' |  awk -F. '{ print $1 }')"
+          echo "::set-output name=minor::$(cat stable/alpine/Dockerfile | awk '$1 == "ENV" && $2 == "NGINX_VERSION" { print $3 }' |  awk -F. '{ print $2 }')"
+          echo "::set-output name=patch::$(cat stable/alpine/Dockerfile | awk '$1 == "ENV" && $2 == "NGINX_VERSION" { print $3 }' |  awk -F. '{ print $3 }')"
+      - name: Build and push NGINX Alpine stable image
+        uses: docker/build-push-action@v2
+        with:
+          platforms: linux/amd64, linux/arm/v6, linux/arm/v7, linux/arm64, linux/386, linux/ppc64le, linux/s390x
+          context: "{{ defaultContext }}:stable/alpine"
+          push: false
+          tags: nginxinc/nginx-unprivileged:${{ steps.version.outputs.major }}.${{ steps.version.outputs.minor }}.${{ steps.version.outputs.patch }}-alpine, nginxinc/nginx-unprivileged:stable-alpine, nginxinc/nginx-unprivileged:${{ steps.version.outputs.major }}.${{ steps.version.outputs.minor }}-alpine, stable/alpine