Add input and output to invoke_agent span.

[antonpirker]

Add the original input for the agent and the final output of the agent to the invoke_agent span.

fixes #4512
fixes PY-1740

[linear]

PY-1740 Add initial input `gen_ai.request.messages` & final output `gen_ai.response.text` to agent invocation span.

[codecov]

Codecov Report

❌ Patch coverage is 82.60870% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.58%. Comparing base (9001126) to head (224a3da).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...k/integrations/openai_agents/spans/invoke_agent.py	80.00%	0 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4785      +/-   ##
==========================================
- Coverage   84.60%   84.58%   -0.02%     
==========================================
  Files         158      158              
  Lines       16463    16479      +16     
  Branches     2850     2855       +5     
==========================================
+ Hits        13928    13939      +11     
- Misses       1694     1695       +1     
- Partials      841      845       +4     

Files with missing lines	Coverage Δ
...dk/integrations/openai_agents/patches/agent_run.py	82.53% <100.00%> (ø)
...k/integrations/openai_agents/spans/invoke_agent.py	87.09% <80.00%> (-6.24%)	⬇️

... and 2 files with indirect coverage changes