[Evals API][10/n] API updates for EvalTaskDef + new test migration (#379)

* wip

* scoring fn api

* eval api

* eval task

* evaluate api update

* pre commit

* unwrap context -> config

* config field doc

* typo

* naming fix

* separate benchmark / app eval

* api name

* rename

* wip tests

* wip

* datasetio test

* delete unused

* fixture

* scoring resolve

* fix scoring register

* scoring test pass

* score batch

* scoring fix

* fix eval

* test eval works

* remove type ignore

* api refactor

* add default task_eval_id for routing

* add eval_id for jobs

* remove type ignore

* only keep 1 run_eval

* fix optional

* register task required

* register task required

* delete old tests

* delete old tests

* fixture return impl

llama_stack/apis/eval_tasks/eval_tasks.py

@@ -0,0 +1,43 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.
+from typing import Any, Dict, List, Literal, Optional, Protocol, runtime_checkable
+
+from llama_models.schema_utils import json_schema_type, webmethod
+
+from pydantic import BaseModel, Field
+
+
+@json_schema_type
+class EvalTaskDef(BaseModel):
+    identifier: str
+    dataset_id: str
+    scoring_functions: List[str]
+    metadata: Dict[str, Any] = Field(
+        default_factory=dict,
+        description="Metadata for this evaluation task",
+    )
+
+
+@json_schema_type
+class EvalTaskDefWithProvider(EvalTaskDef):
+    type: Literal["eval_task"] = "eval_task"
+    provider_id: str = Field(
+        description="ID of the provider which serves this dataset",
+    )
+
+
+@runtime_checkable
+class EvalTasks(Protocol):
+    @webmethod(route="/eval_tasks/list", method="GET")
+    async def list_eval_tasks(self) -> List[EvalTaskDefWithProvider]: ...
+
+    @webmethod(route="/eval_tasks/get", method="GET")
+    async def get_eval_task(self, name: str) -> Optional[EvalTaskDefWithProvider]: ...
+
+    @webmethod(route="/eval_tasks/register", method="POST")
+    async def register_eval_task(
+        self, eval_task_def: EvalTaskDefWithProvider
+    ) -> None: ...