feat(nextjs): Add mechanism to withSentry-caught errors (#4046)

Author: lobsterkatie

packages/nextjs/src/utils/withSentry.ts

@@ -79,6 +79,7 @@ export const withSentry = (handler: NextApiHandler): WrappedNextApiHandler => {
         if (currentScope) {
           currentScope.addEventProcessor(event => {
             addExceptionMechanism(event, {
+              mechanism: 'withSentry',
               handled: false,
             });
             return event;