Add httpx instrumentation (#600)

Author: cecheta

code/app.py

@@ -1,6 +1,8 @@
 from azure.monitor.opentelemetry import configure_azure_monitor
+from opentelemetry.instrumentation.httpx import HTTPXClientInstrumentor
 
 configure_azure_monitor()
+HTTPXClientInstrumentor().instrument()  # httpx is used by openai
 
 from create_app import create_app  # noqa: E402