docs(js): Add OpenTelemetry JS v3 example to custom OpenTelemetry setup

docs/platforms/javascript/common/opentelemetry/custom-setup.mdx

@@ -16,9 +16,40 @@ Initialize your OpenTelemetry provider before calling `Sentry.init()`.
 
 Add an OTLP exporter to your existing provider. Install `@opentelemetry/exporter-trace-otlp-http` if you do not already use it. `Sentry.getOtlpTracesEndpoint()` supplies the endpoint URL and authentication headers for your DSN.
 
-This example uses `NodeTracerProvider`. Add the same span processor to `spanProcessors` if you use `NodeSDK` instead. Keep your existing sampler, propagator, context manager, and instrumentation; do not register a second provider.
+Pick the tab that matches your OpenTelemetry JS version. Keep your existing sampler, propagator, context manager, and instrumentation; do not register a second provider.
 
-```javascript {filename: instrument.mjs}
+```javascript {tabTitle:OpenTelemetry JS v3} {filename: instrument.mjs}
+import * as Sentry from "___SDK_PACKAGE___";
+import { OTLPTraceExporter } from "@opentelemetry/exporter-trace-otlp-http";
+import { NodeSDK } from "@opentelemetry/sdk-node";
+import { BatchSpanProcessor } from "@opentelemetry/sdk-trace";
+
+const dsn = "___PUBLIC_DSN___";
+const endpoint = Sentry.getOtlpTracesEndpoint(dsn);
+
+if (!endpoint) {
+  throw new Error("Could not parse the Sentry DSN");
+}
+
+const sdk = new NodeSDK({
+  spanProcessors: [
+    new BatchSpanProcessor({ exporter: new OTLPTraceExporter(endpoint) }),
+    // Keep any other span processors you already use.
+  ],
+  // Keep your existing instrumentations, sampler, and propagator.
+});
+
+sdk.start();
+
+Sentry.init({
+  dsn,
+  enableOpenTelemetrySetup: false,
+  // Leave tracesSampleRate and tracesSampler unset. OpenTelemetry owns tracing.
+  integrations: [Sentry.openTelemetryIntegration()],
+});
+```
+
+```javascript {tabTitle:OpenTelemetry JS v2} {filename: instrument.mjs}
 import * as Sentry from "___SDK_PACKAGE___";
 import { OTLPTraceExporter } from "@opentelemetry/exporter-trace-otlp-http";
 import { BatchSpanProcessor } from "@opentelemetry/sdk-trace-base";
@@ -50,7 +81,7 @@ Sentry.init({
 
 ## Use Sentry for Error Monitoring Only
 
-If your traces go elsewhere, keep your existing OpenTelemetry exporter and omit the Sentry OTLP exporter from the example above. The `Sentry.init()` configuration stays the same. `openTelemetryIntegration()` links Sentry errors to the active OpenTelemetry trace without sending spans to Sentry.
+If your traces go elsewhere, keep your existing OpenTelemetry exporter and omit the Sentry OTLP exporter from the examples above. The `Sentry.init()` configuration stays the same. `openTelemetryIntegration()` links Sentry errors to the active OpenTelemetry trace without sending spans to Sentry.
 
 ## Configure Sampling