added workflow to publish docker images

.github/workflows/publish_docker_images.yml

@@ -0,0 +1,50 @@
+name: Publish JupyterHub Docker images on DockerHub
+on: 
+  push: 
+    paths: 
+      - 'dockerfiles/dsci-student/Dockerfile'
+      - 'dockerfiles/dsci-grading/Dockerfile'
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@master
+    - uses: actions/checkout@master
+      with:
+        fetch-depth: '0'
+    - name: Bump version and push tag
+      uses: anothrNick/[email protected]
+      env:
+        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        WITH_V: true
+      id: bump
+    - name: Create Release
+      id: create_release
+      uses: actions/create-release@v1
+      env:
+        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }} # This token is provided by Actions, you do not need to create your own token
+      with:
+        tag_name: ${{ steps.bump.outputs.new_tag }}
+        release_name: ${{ steps.bump.outputs.new_tag }}
+        body: |
+          Changes in this Release
+          - Rebuilt r-dsci-100 Docker image and published to DockerHub with new tag
+          - Rebuilt r-dsci-grading Docker image and published to DockerHub with new tag
+        draft: false
+        prerelease: false
+    - name: Publish to Registry
+      uses: elgohr/Publish-Docker-Github-Action@master
+      with:
+        name: ubcstat/dsci-student
+        username: ${{ secrets.DOCKER_USERNAME }}
+        password: ${{ secrets.DOCKER_PASSWORD }}
+        workdir: dockerfiles/dsci-student
+        tags: "${{ steps.bump.outputs.new_tag }}"
+    - name: Publish to Registry
+      uses: elgohr/Publish-Docker-Github-Action@master
+      with:
+        name: ubcdsci/dsci-grading
+        username: ${{ secrets.DOCKER_USERNAME }}
+        password: ${{ secrets.DOCKER_PASSWORD }}
+        workdir: dockerfiles/dsci-grading
+        tags: "${{ steps.bump.outputs.new_tag }}"