Add OTLP traces intake endpoint preview note (#34724)

* Add OTLP traces intake endpoint preview note

Indicate that the OTLP traces intake endpoint is in Preview
and direct customers to Datadog support for access.

* Update OTLP traces intake endpoint description

Author: brett0000FF

content/en/opentelemetry/setup/otlp_ingest/_index.md

@@ -21,6 +21,7 @@ You might prefer this option if you're looking for a straightforward setup and w
 
 - [OTLP logs intake endpoint][3]
 - [OTLP metrics intake endpoint][4]
+- OTLP traces intake endpoint (in Preview): To request access, contact [Datadog support][5].
 
 ## Further reading
 
@@ -30,3 +31,4 @@ You might prefer this option if you're looking for a straightforward setup and w
 [2]: /opentelemetry/setup/collector_exporter/
 [3]: /opentelemetry/setup/intake_endpoint/otlp_logs
 [4]: /opentelemetry/setup/intake_endpoint/otlp_metrics
+[5]: /help/