CI: add a timed trigger and a manual trigger ...

* timed trigger: runs every 5 days
* manual trigger: manually starts the website build

.github/workflows/deploy.yml

@@ -5,6 +5,10 @@ on:
     branches: [ hugo ]
   pull_request:
     branches: [ hugo ]
+  schedule:
+    - cron: '35 0 */5 * *'
+  workflow_dispatch:
+    inputs:
 
 jobs:
   build: