Add SMTP password field.

Added a password field to the Mail Settings tab in the General Settings panel, ensuring it is saved and retrieved via the `/api/settings` endpoint.

application/src/services/settingsService.ts

@@ -36,6 +36,7 @@ export interface GeneralSettings {
     port?: number;
     host?: string;
     username?: string;
+    password?: string;
     authMethod?: string;
     tls?: boolean;
     localName?: string;