feat: [New Eval Benchamark] IfEval (#1708)

# What does this PR do?
In this PR, we added a new eval open benchmark IfEval based on paper
https://arxiv.org/abs/2311.07911 to measure the model capability of
instruction following.


## Test Plan
spin up a llama stack server with open-benchmark template

run `llama-stack-client --endpoint xxx eval run-benchmark
"meta-reference-ifeval" --model-id "meta-llama/Llama-3.3-70B-Instruct"
--output-dir "/home/markchen1015/" --num-examples 20` on client side and
get the eval aggregate results

llama_stack/templates/open-benchmark/open_benchmark.py

@@ -203,6 +203,13 @@ def get_distribution_template() -> DistributionTemplate:
                 uri="huggingface://datasets/llamastack/bfcl_v3?split=train",
             ),
         ),
+        DatasetInput(
+            dataset_id="ifeval",
+            purpose=DatasetPurpose.eval_messages_answer,
+            source=URIDataSource(
+                uri="huggingface://datasets/llamastack/IfEval?split=train",
+            ),
+        ),
         DatasetInput(
             dataset_id="docvqa",
             purpose=DatasetPurpose.eval_messages_answer,
@@ -238,6 +245,11 @@ def get_distribution_template() -> DistributionTemplate:
             dataset_id="bfcl",
             scoring_functions=["basic::bfcl"],
         ),
+        BenchmarkInput(
+            benchmark_id="meta-reference-ifeval",
+            dataset_id="ifeval",
+            scoring_functions=["basic::ifeval"],
+        ),
         BenchmarkInput(
             benchmark_id="meta-reference-docvqa",
             dataset_id="docvqa",