Python: Fix observability samples (#5016)

* Fix observability samples

* Update python/samples/02-agents/observability/configure_otel_providers_with_parameters.py

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update python/samples/02-agents/observability/agent_observability.py

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update python/samples/02-agents/observability/agent_observability.py

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

python/samples/02-agents/observability/agent_observability.py

@@ -7,6 +7,7 @@ from typing import Annotated
 from agent_framework import Agent, tool
 from agent_framework.foundry import FoundryChatClient
 from agent_framework.observability import configure_otel_providers, get_tracer
+from azure.identity import AzureCliCredential
 from dotenv import load_dotenv
 from opentelemetry.trace import SpanKind
 from opentelemetry.trace.span import format_trace_id
@@ -18,6 +19,12 @@ load_dotenv()
 """
 This sample shows how you can observe an agent in Agent Framework by using the
 same observability setup function.
+
+Pre-requisites:
+- A Foundry project
+- An observability backend to receive traces and metrics (for example, a local or remote
+  OpenTelemetry Collector, another OTLP-compatible backend, or console exporters enabled
+  via environment variables).
 """
 
 
@@ -47,7 +54,7 @@ async def main():
         print(f"Trace ID: {format_trace_id(current_span.get_span_context().trace_id)}")
 
         agent = Agent(
-            client=FoundryChatClient(),
+            client=FoundryChatClient(credential=AzureCliCredential()),
             tools=get_weather,
             name="WeatherAgent",
             instructions="You are a weather assistant.",