Fix lambda handler name export

Author: francisco-videira-nhs

lambdas/upsert-letter/src/index.ts

@@ -3,5 +3,5 @@ import createUpsertLetterHandler from "./handler/upsert-handler";
 
 const container = createDependenciesContainer();
 
+// eslint-disable-next-line import-x/prefer-default-export
 export const upsertLetterHandler = createUpsertLetterHandler(container);
-export default upsertLetterHandler;