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.

service/epay.go

@@ -1,12 +1,12 @@
 package service
 
 import (
-	"one-api/constant"
+	"one-api/setting"
 )
 
 func GetCallbackAddress() string {
-	if constant.CustomCallbackAddress == "" {
-		return constant.ServerAddress
+	if setting.CustomCallbackAddress == "" {
+		return setting.ServerAddress
 	}
-	return constant.CustomCallbackAddress
+	return setting.CustomCallbackAddress
 }