refactor: extract cors configs into dify config and cleanup the config class (#5507)

Co-authored-by: takatost <takatost@gmail.com>

api/app.py

@@ -24,7 +24,6 @@ from flask_cors import CORS
 from werkzeug.exceptions import Unauthorized
 
 from commands import register_commands
-from config import Config
 
 # DO NOT REMOVE BELOW
 from events import event_handlers
@@ -82,7 +81,6 @@ def create_flask_app_with_configs() -> Flask:
     with configs loaded from .env file
     """
     dify_app = DifyApp(__name__)
-    dify_app.config.from_object(Config())
     dify_app.config.from_mapping(DifyConfig().model_dump())
     return dify_app
 
@@ -232,7 +230,7 @@ def register_blueprints(app):
 app = create_app()
 celery = app.extensions["celery"]
 
-if app.config['TESTING']:
+if app.config.get('TESTING'):
     print("App is running in TESTING mode")