[googlemanagedprometheusexporter] Clarify support status of this expo…

…rter (open-telemetry#28863)

*   Link to related GCP docs
*   Clarify mention of "traces"
* Drop mention of PromQL support as a difference from `googlecloud`
exporter

exporter/googlemanagedprometheusexporter/README.md

@@ -13,9 +13,7 @@
 [observiq]: https://github.com/observIQ/observiq-otel-collector
 <!-- end autogenerated section -->
 
-This exporter can be used to send metrics and traces to [Google Cloud Managed Service for Prometheus](https://cloud.google.com/stackdriver/docs/managed-prometheus).  The difference between this exporter and the `googlecloud` exporter is that metrics sent with this exporter are queried using [promql](https://prometheus.io/docs/prometheus/latest/querying/basics/#querying-prometheus), rather than standard the standard MQL.
-
-This exporter is not the standard method of ingesting metrics into Google Cloud Managed Service for Prometheus, which is built on a drop-in replacement for the Prometheus server: https://github.com/GoogleCloudPlatform/prometheus.  This exporter does not support the full range of Prometheus functionality, including the UI, recording and alerting rules, and can't be used with the GMP Operator, but does support sending metrics.
+This exporter can be used to send metrics (including trace exemplars) to [Google Cloud Managed Service for Prometheus](https://cloud.google.com/stackdriver/docs/managed-prometheus). It is one of [several supported approaches for sending metrics to Google Cloud Managed Service for Prometheus](https://cloud.google.com/stackdriver/docs/managed-prometheus#gmp-data-collection).
 
 ## Configuration Reference