Update documentation for span.setStatus method (#14116)

The documentation in
`platform-includes/distributed-tracing/custom-instrumentation/javascript.mdx`
was updated to correct the usage of `span.setStatus`.

*   Previously, `span.setStatus({ code: 'error' });` was used.
* This has been changed to `span.setStatus({ code: 2, message: 'error'
});`.

This modification aligns the documentation with the Sentry JavaScript
SDK's `SpanStatus` interface, which expects a numerical `code`
(following OpenTelemetry standards) rather than a string. The numerical
code `2` signifies an 'error' status. This ensures that `span.setStatus`
correctly updates the span's status, resolving issues where the status
was not visually reflected due to incorrect API parameter types.

Co-authored-by: Cursor Agent <cursoragent@cursor.com>

Author: AbhiPrasad

platform-includes/distributed-tracing/custom-instrumentation/javascript.mdx

@@ -108,7 +108,7 @@ function sentryInterceptor(methodDescriptor, nextCall) {
       if (span) {
         // Update status based on the gRPC result
         if (status.code !== grpc.status.OK) {
-          span.setStatus({ code: 'error' });
+          span.setStatus({ code: 2, message: 'error' });
           span.setAttribute('grpc.status_code', status.code);
           span.setAttribute('grpc.status_description', status.details);
         }