Mention client reports in Logs dev docs (#15541)

Added section on client reports for discarded log messages.

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Author: adinauer

develop-docs/sdk/telemetry/logs.mdx

@@ -687,3 +687,7 @@ Example:
 : **String, optional**. The time the log was created in Unix nanoseconds. If not set, the SDK should set this to the current time.
 
 </Expandable>
+
+## Client Reports
+
+SDKs must report count (`log_item`) and size in bytes (`log_byte`) of discarded log messages. An approximation of log size is sufficient (e.g. by counting as if serialized).