docs: small clarification re: structured metadata (backport release-3…

….1.x) (#15230)

Co-authored-by: J Stickler <[email protected]>

docs/sources/send-data/otel/_index.md

@@ -16,7 +16,7 @@ For ingesting logs to Loki using the OpenTelemetry Collector, you must use the [
 
 When logs are ingested by Loki using an OpenTelemetry protocol (OTLP) ingestion endpoint, some of the data is stored as [Structured Metadata]({{< relref "../../get-started/labels/structured-metadata" >}}).
 
-You must set `allow_structured_metadata` to `true` within your Loki config file. Otherwise, Loki will reject the log payload as malformed.
+You must set `allow_structured_metadata` to `true` within your Loki config file. Otherwise, Loki will reject the log payload as malformed.  Note that Structured Metadata is enabled by default in Loki 3.0 and later.
 
 ```yaml
 limits_config: