Allow starting khoj in non-GUI mode without config file instantiated

- Start khoj server (in non-GUI mode) without needing config file
  already instantiated.
  - But throw warning to configure khoj to use it
- This allows plugins to configure the app via the /config/data APIs
- To be used by the Khoj obsidian plugin to configure markdown content
  in khoj

src/configure.py

@@ -26,9 +26,10 @@ logger = logging.getLogger(__name__)
 def configure_server(args, required=False):
     if args.config is None:
         if required:
-            print('Exiting as Khoj is not configured. Configure the application to use it.')
+            logger.error(f'Exiting as Khoj is not configured.\nConfigure it via GUI or by editing {state.config_file}.')
             sys.exit(1)
         else:
+            logger.warn(f'Khoj is not configured.\nConfigure it via khoj GUI, plugins or by editing {state.config_file}.')
             return
     else:
         state.config = args.config