added workflow to trigger new docker images on release (#2882)

.github/workflows/docker.yaml

@@ -0,0 +1,17 @@
+name: 'Docker Build'
+on:
+  release:
+    types: [released]
+
+jobs:
+  build:
+    name: Dispatch release event to tobybatch
+    runs-on: ubuntu-latest
+    steps:
+      - name: Emit repository_dispatch
+        uses: mvasigh/dispatch-action@1.1.6
+        with:
+          token: ${{ secrets.DOCKER_ACCESS_TOKEN }}
+          repo: kimai2
+          owner: tobybatch
+          event_type: kimai_release