Mark OTLP Logs Stable

Proto stability is declared here open-telemetry/opentelemetry-proto#376

Author: tigrannajaryan

CHANGELOG.md

@@ -26,6 +26,8 @@ release.
 
 ### Logs
 
+- OTLP Logs are now Stable.
+
 ### Resource
 
 ### Semantic Conventions

specification/protocol/otlp.md

@@ -54,7 +54,7 @@ own maturity level, which in turn applies to **all** the OTLP Transports listed
 
 * Tracing: **Stable**
 * Metrics: **Stable**
-* Logs: **Beta**
+* Logs: **Stable**
 
 See [OTLP Maturity Level](https://github.com/open-telemetry/opentelemetry-proto#maturity-level).