[Monitor exporter] Update OT Exporter to latest spec changes (Azure#20770)

Author: lzchen

sdk/monitor/azure-monitor-opentelemetry-exporter/README.md

@@ -21,7 +21,7 @@ To use this package, you must have:
 * Azure subscription - [Create a free account][azure_sub]
 * Azure Monitor - [How to use application insights][application_insights_namespace]
 * Opentelemetry SDK - [Opentelemtry SDK for Python][ot_sdk_python]
-* Python 3.5 or later - [Install Python][python]
+* Python 3.6 or later - [Install Python][python]
 
 ### Instantiate the client