Allow passing in additional plugins for evals

Right now EvaluationGenerator just has the two baked in plugins _RequestIntercepterPlugin and EnsureRetryOptionsPlugin. I would like to also have the ReflectAndRetryPlugin here.

**Describe the solution you'd like**
Allow for arbitrary plugins to be added for evals.

**Describe alternatives you've considered**
Add ReflectAndRetry on the eval runner. Not as robust and some might not want this.