feat: Introduce settings package and refactor constants

- Added a new `setting` package to replace the `constant` package for configuration management, improving code organization and clarity.
- Moved various configuration variables such as `ServerAddress`, `PayAddress`, and `SensitiveWords` to the new `setting` package.
- Updated references throughout the codebase to use the new `setting` package, ensuring consistent access to configuration values.
- Introduced new files for managing chat settings and midjourney settings, enhancing modularity and maintainability of the code.

setting/payment.go

@@ -0,0 +1,8 @@
+package setting
+
+var PayAddress = ""
+var CustomCallbackAddress = ""
+var EpayId = ""
+var EpayKey = ""
+var Price = 7.3
+var MinTopUp = 1