Setup image build/push GHA

.github/workflows/ci-image-build-push.yaml

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+name: image-build
+
+on:
+  release:
+    # Dynamic releasetag tag is set based on the assumption this ci task only runs on release
+    types: [published]
+
+# Variables to be used throughout the workflow manifest
+env:
+  # TO-DO (@phenixblue): Need to investigate more into why the `linux/ppc64le` 
+  # platform has issues with installing Python dependencies during image build.
+  #
+  # Removing for now to not block
+  TARGET_PLATFORMS: linux/amd64,linux/arm64
+jobs:
+
+  # Build and push imageswap-init container image
+  build-and-push-image:
+    name: Build and push TWR Tools image to DockerHub
+    runs-on: ubuntu-latest
+
+    steps:
+
+      - name: Check out the repo
+        uses: actions/checkout@v2
+
+      # Collect Release Tag is used to to collect information needed later in the action and expose it so it can be referenced
+      - name: Collect Release Tag
+        id: prep
+        # GITHUB_REF variable must exist in action; this may rely on {{ on: release: types: [published] }} gating the action
+        run: |
+          echo ::set-output name=releasetag::${GITHUB_REF#refs/tags/}
+
+      # Setup QEMU to support multi-arch builds
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v1
+
+      # Part of docker/build-push-action@v2; setting up the build system
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+
+      # Part of docker/build-push-action@v2; login to dockerhub
+      - name: Login to DockerHub
+        uses: docker/login-action@v1
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_PASSWORD }}
+
+      - name: Build and push imageswap-init image to DockerHub
+        if: github.repository == 'phenixblue/twrtools'
+        timeout-minutes: 30
+        uses: docker/build-push-action@v2
+        with:
+          context: ./
+          # file should be specified relative to the repo root rather than relative to the context
+          file: ./Dockerfile
+          # Defines the target platform architectures images should be built for
+          platforms: ${{ env.TARGET_PLATFORMS }}
+          # push is no longer defaulted to true under v2; to push you must specify push is true
+          push: true
+          # Uses the releasetag output exposed by the Collect Release Tag step to set the tag under v2
+          tags: jmsearcy/twrtools:${{ steps.prep.outputs.releasetag }},jmsearcy/twrtools:latest