Add Github Action to build and push to Docker Hub

.github/workflows/build-docker.yml

@@ -0,0 +1,41 @@
+name: Build and push to DockerHub
+on: [ push, pull_request ]
+jobs:
+  docker:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Inject slug/short environment variables
+      uses: rlespinasse/github-slug-action@v3.x
+    - name: Decide whether to push to DockerHub, and set tag
+      if: |
+        github.event_name == 'push' &&
+        ( startsWith( env.GITHUB_REF, 'refs/tags/' ) ||
+          contains( fromJSON('["master","develop","testnet","hardfork"]'), env.GITHUB_REF_NAME ) )
+      run: |
+        echo "DOCKER_PUSH_TAG=${GITHUB_REF_NAME}"
+        echo "DOCKER_PUSH_TAG=${GITHUB_REF_NAME}" >> $GITHUB_ENV
+    - name: Test tag
+      if: env.DOCKER_PUSH_TAG != ''
+      run: echo "${DOCKER_PUSH_TAG}"
+    - name: Checkout
+      uses: actions/checkout@v2
+    - name: Set up Docker Buildx
+      uses: docker/setup-buildx-action@v1
+    - name: Build only
+      uses: docker/build-push-action@v2
+      with:
+        context: .
+        load: true
+    - name: Login to DockerHub
+      if: env.DOCKER_PUSH_TAG != ''
+      uses: docker/login-action@v1
+      with:
+        username: ${{ secrets.DOCKERHUB_USERNAME }}
+        password: ${{ secrets.DOCKERHUB_TOKEN }}
+    - name: Push to DockerHub
+      if: env.DOCKER_PUSH_TAG != ''
+      uses: docker/build-push-action@v2
+      with:
+        context: .
+        push: true
+        tags: bitshares/bitshares-core:${{ env.DOCKER_PUSH_TAG }}