Add an example script to run lighteval based evaluation

[dongwang218]

Why ?

add an example to showcase integration with lighteval

How ?

via litellm and openai comptabile api

Test plan

python scripts/light_eval_example.py  --cleanup True --max_samples 10
██| 1/1 [00:00<00:00, 521.87ba/s]
|        Task        |Version|    Metric     |Value|   |Stderr|
|--------------------|-------|---------------|----:|---|-----:|
|all                 |       |pass@k_with_k&n|  0.4|±  |0.1633|
|lighteval:math_500:0|       |pass@k_with_k&n|  0.4|±  |0.1633|

Running command: scancel 10940707 10940709
cluster lighteval_test shutdown