Setup solr schema and index all data using a system task

The task runs on application start. It sets the schema using solr's
schema api and then indexes all data in the database. Each step is
memorized so that it is not executed again on subsequent starts.

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

@@ -153,6 +153,7 @@ docspell.server {
       enabled = true
       solr = {
         url = "http://localhost:8983/solr/docspell_core"
+        commit-within = 1000
       }
     }
   }