trigger docker workflow on release

Signed-off-by: Andy Miller <rhuk@mac.com>

.github/workflows/trigger-docker.yml

@@ -0,0 +1,32 @@
+name: Trigger Docker Build
+
+on:
+  # Trigger when a release is published
+  release:
+    types: [published]
+
+  # Manual trigger
+  workflow_dispatch:
+    inputs:
+      channel:
+        description: 'Grav channel'
+        required: true
+        default: 'stable'
+        type: choice
+        options:
+          - stable
+          - beta
+
+jobs:
+  trigger:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Trigger docker-grav build
+        run: |
+          curl -X POST \
+            -H "Accept: application/vnd.github+json" \
+            -H "Authorization: Bearer ${{ secrets.GLOBAL_TOKEN }}" \
+            -H "X-GitHub-Api-Version: 2022-11-28" \
+            https://api.github.com/repos/getgrav/docker-grav/dispatches \
+            -d '{"event_type":"grav-release","client_payload":{"channel":"${{ inputs.channel || 'stable' }}"}}'
+          echo "Dispatched docker-grav build"