Run file integrity check in house keeping tasks

modules/joex/src/main/resources/reference.conf

@@ -194,6 +194,11 @@ docspell.joex {
       # How often the node must be unreachable, before it is removed.
       min-not-found = 2
     }
+
+    # Checks all files against their checksum
+    integrity-check {
+      enabled = true
+    }
   }
 
   # A periodic task to check for new releases of docspell. It can