Update tracing.md with Agenta (#1541)

Updating external tracing processor lists and added Agenta and linked a
tutorial for integration

Author: mmabrouk

docs/tracing.md

@@ -146,3 +146,5 @@ agent = Agent(
 -   [Galileo](https://v2docs.galileo.ai/integrations/openai-agent-integration#openai-agent-integration)
 -   [Portkey AI](https://portkey.ai/docs/integrations/agents/openai-agents)
 -   [LangDB AI](https://docs.langdb.ai/getting-started/working-with-agent-frameworks/working-with-openai-agents-sdk)
+-   [Agenta](https://docs.agenta.ai/observability/integrations/openai-agents)
+