[FT] showing count in Markdown summary table

## Issue encountered

I am seeing this output from `lighteval endpoint litellm` with `lighteval==0.10.0`:

```none
| Task |Version| Metric |Value| |Stderr|
|------------------------|------:|---------------|----:|---|-----:|
|all | |ether0_accuracy| 0|± | 0|
|community:ether0:loose:0| 0|ether0_accuracy| 0|± | 0|
```

At a glance, it's unclear if I have misconfigured `LightevalTaskConfig.hf_filter`, or if accuracy truly was 0%.

(Note: in actuality, there were 10 questions, all incorrect.)

## Solution/Feature

Showing a count of questions run, to clarify the size of the evaluation.

## Possible alternatives

None