feat(destinations): add additionalFlags field for destination settings

- Introduced an optional `additionalFlags` field in the destination schema to allow users to specify extra parameters.
- Updated the form in the dashboard to include a textarea for entering additional flags.
- Modified the API router to handle the new `additionalFlags` input when creating or updating destinations.
- Adjusted database schema to accommodate the new field in the destination table.

packages/server/src/utils/backups/utils.ts

@@ -79,6 +79,10 @@ export const getS3Credentials = (destination: Destination) => {
 		rcloneFlags.unshift(`--s3-provider="${provider}"`);
 	}
 
+	if (destination.additionalFlags?.length) {
+		rcloneFlags.push(...destination.additionalFlags);
+	}
+
 	return rcloneFlags;
 };