Create action to build Docker images (#2020)

Update them every two weeks

Signed-off-by: Igor Pecovnik <igor.pecovnik@gmail.com>

.github/workflows/build-and-upload-docker-image-to-hub.yml

@@ -0,0 +1,20 @@
+name: Build Docker image
+# This workflow is triggered 1st, 16th and 31st
+on:
+  schedule:
+    - cron: '0 0 */15 * *'
+jobs:
+  build:
+    name: latest
+    runs-on: ubuntu-latest
+    steps:
+     - uses: actions/checkout@v1
+     - name: Login to DockerHub Registry
+       run: echo ${{ secrets.DOCKERHUB_PASSWORD }} | docker login -u ${{ secrets.DOCKERHUB_USERNAME }} --password-stdin   
+     - name: Build Docker image
+       run: |
+        echo "latest" > VERSION
+        ./compile.sh docker KERNEL_ONLY="yes" BOARD="bananapi" BRANCH="current" KERNEL_CONFIGURE="no"        
+     - name: Push Docker image
+       run: docker push armbian/build:latest
+