add docker build on github, get rid of gitlab

.github/workflows/docker.yml

@@ -0,0 +1,28 @@
+name: Docker Production build
+
+on:
+  push:
+    branches: [ master ]
+
+jobs:
+  build-amd64:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        architecture: [amd64]
+    steps:
+    - name: Login to DockerHub
+      uses: docker/login-action@v2
+      with:
+        username: ${{ secrets.DOCKERHUB_USERNAME }}
+        password: ${{ secrets.DOCKERHUB_TOKEN }}
+    - name: Checkout
+      uses: actions/checkout@v3
+    - name: Set up QEMU
+      uses: docker/setup-qemu-action@v2
+    - name: Set up Docker Buildx
+      uses: docker/setup-buildx-action@v2
+    - name: Available platforms
+      run: echo ${{ steps.buildx.outputs.platforms }}
+    - name: Run Buildx
+      run: docker buildx build --platform linux/${{matrix.architecture}} -t kerberos/documentation:$(echo $GITHUB_SHA | cut -c1-7) --push .