Improve logging configuration

- Log levels of specific loggers can be defined in the config
  file (doesn't work with env variables)

- Log events of background tasks carry now additional data

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

@@ -29,7 +29,15 @@ docspell.server {
 
     # The minimum level to log. From lowest to highest:
     # Trace, Debug, Info, Warn, Error
-    minimum-level = "Info"
+    minimum-level = "Warn"
+
+    # Override the log level of specific loggers
+    levels = {
+      "docspell" = "Info"
+      "org.flywaydb" = "Info"
+      "binny" = "Info"
+      "org.http4s" = "Info"
+    }
   }
 
   # Where the server binds to.