Switch to GitHub App Installation token authentication

Author: klutchell

.github/workflows/flowzone.yml

@@ -27,12 +27,13 @@ jobs:
         github.event_name == 'push'
       )
     secrets:
-      FLOWZONE_TOKEN: ${{ secrets.FLOWZONE_TOKEN }}
+      GH_APP_PRIVATE_KEY: ${{ secrets.GH_APP_PRIVATE_KEY }}
       DOCKERHUB_USER: ${{ secrets.DOCKERHUB_USER }}
       DOCKERHUB_TOKEN: ${{ secrets.DOCKERHUB_TOKEN }}
     with:
       disable_versioning: true
       toggle_auto_merge: false
+      token_retrieval_mode: user
       docker_images: |
         ghcr.io/klutchell/dnscrypt-proxy,
         docker.io/klutchell/dnscrypt-proxy