Fix secret key inconsistency cross the RAGFlow servers (#14591)

### What problem does this PR solve?

A and B, two API servers and a REDIS server.
If A and REDIS restart, B will hold the obsolete secret key and will
lead to error.

TODO:
app.config['SECRET_KEY'] and app.secret_key still hold obsolete secret
key.

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

---------

Signed-off-by: Jin Hai <haijin.chn@gmail.com>

api/db/db_models.py

@@ -726,7 +726,7 @@ class User(DataBaseModel, AuthUser):
         return self.email
 
     def get_id(self):
-        jwt = Serializer(secret_key=settings.SECRET_KEY)
+        jwt = Serializer(secret_key=settings.get_secret_key())
         return jwt.dumps(str(self.access_token))
 
     class Meta: