Add GitHub Action to publish docker image

.github/workflows/docker-image.yml

@@ -0,0 +1,18 @@
+name: Publish Docker Image on Tag
+on:
+  push:
+    tags: '*'
+jobs:
+  build_and_publish:
+    runs-on: ubuntu-latest
+    steps:
+      - name: 'Checkout git repo'
+        uses: actions/checkout@v1
+      - name: Publish Docker Image on Tag
+        uses: docker/build-push-action@v1
+        with:
+          username: ${{ secrets.DOCKER_USERNAME }}
+          password: ${{ secrets.DOCKER_PASSWORD }}
+          repository: genomenexus/genome-nexus-vep
+          tag_with_ref: true
+          push: ${{ startsWith(github.ref, 'refs/tags/') }}