Fix race condition in ConfigCommand and implement user-specific menu restrictions

[coderabbitai]

Issue Description

Race Condition in ConfigCommand

There's a potential concurrency race condition in when multiple users interact with the configuration menu simultaneously. When multiple users confirm or cancel concurrently, the config could be updated or overwritten unpredictably.

User-Specific Menu Access

Menus should have an option to only be usable by the person who initiated them to prevent unauthorized modifications.

Suggested Solutions

1. Implement synchronization for config writes
2. Add a feature flag for menus to restrict access to the original invoker
3. Add user validation in the menu handler logic

References

• PR: Move to using JSON config for guilds. #41
• Comment: Move to using JSON config for guilds. #41 (comment)

cc @Scyye