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/apps/__init__.py

@@ -79,8 +79,8 @@ app.config["SESSION_REDIS"] = settings.decrypt_database_config(name="redis")
 app.config["MAX_CONTENT_LENGTH"] = int(
     os.environ.get("MAX_CONTENT_LENGTH", 1024 * 1024 * 1024)
 )
-app.config['SECRET_KEY'] = settings.SECRET_KEY
-app.secret_key = settings.SECRET_KEY
+app.config['SECRET_KEY'] = settings.get_secret_key()
+app.secret_key = settings.get_secret_key()
 commands.register_commands(app)
 
 from functools import wraps
@@ -93,7 +93,7 @@ P = ParamSpec("P")
 
 
 def _load_user():
-    jwt = Serializer(secret_key=settings.SECRET_KEY)
+    jwt = Serializer(secret_key=settings.get_secret_key())
     authorization = request.headers.get("Authorization")
     g.user = None
     if not authorization: