Adopt to new loggin api

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

@@ -21,6 +21,17 @@ docspell.server {
   # other nodes can reach this server.
   internal-url = "http://localhost:7880"
 
+  # Configures logging
+  logging {
+    # The format for the log messages. Can be one of:
+    # Json, Logfmt, Fancy or Plain
+    format = "Json"
+
+    # The minimum level to log. From lowest to highest:
+    # Trace, Debug, Info, Warn, Error
+    minimumLevel = "Debug"
+  }
+
   # Where the server binds to.
   bind {
     address = "localhost"