feat: Add NVIDIA NeMo datastore (#1852)

# What does this PR do?
Implemetation of NeMO Datastore register, unregister API.

Open Issues: 
- provider_id gets set to `localfs` in client.datasets.register() as it
is specified in routing_tables.py: DatasetsRoutingTable
see: #1860

Currently I have passed `"provider_id":"nvidia"` in metadata and have
parsed that in `DatasetsRoutingTable`
(Not the best approach, but just a quick workaround to make it work for
now.)

## Test Plan
- Unit test cases: `pytest
tests/unit/providers/nvidia/test_datastore.py`
```bash
========================================================== test session starts ===========================================================
platform linux -- Python 3.10.0, pytest-8.3.5, pluggy-1.5.0
rootdir: /home/ubuntu/llama-stack
configfile: pyproject.toml
plugins: anyio-4.9.0, asyncio-0.26.0, nbval-0.11.0, metadata-3.1.1, html-4.1.1, cov-6.1.0
asyncio: mode=strict, asyncio_default_fixture_loop_scope=None, asyncio_default_test_loop_scope=function
collected 2 items                                                                                                                        

tests/unit/providers/nvidia/test_datastore.py ..                                                                                   [100%]

============================================================ warnings summary ============================================================

====================================================== 2 passed, 1 warning in 0.84s ======================================================
```

cc: @dglogo, @mattf, @yanxi0830

llama_stack/providers/remote/datasetio/nvidia/config.py

@@ -0,0 +1,61 @@
+# 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.
+
+import os
+import warnings
+from typing import Any, Dict, Optional
+
+from pydantic import BaseModel, Field
+
+
+class NvidiaDatasetIOConfig(BaseModel):
+    """Configuration for NVIDIA DatasetIO implementation."""
+
+    api_key: Optional[str] = Field(
+        default_factory=lambda: os.getenv("NVIDIA_API_KEY"),
+        description="The NVIDIA API key.",
+    )
+
+    dataset_namespace: Optional[str] = Field(
+        default_factory=lambda: os.getenv("NVIDIA_DATASET_NAMESPACE", "default"),
+        description="The NVIDIA dataset namespace.",
+    )
+
+    project_id: Optional[str] = Field(
+        default_factory=lambda: os.getenv("NVIDIA_PROJECT_ID", "test-project"),
+        description="The NVIDIA project ID.",
+    )
+
+    datasets_url: str = Field(
+        default_factory=lambda: os.getenv("NVIDIA_DATASETS_URL", "http://nemo.test"),
+        description="Base URL for the NeMo Dataset API",
+    )
+
+    # warning for default values
+    def __post_init__(self):
+        default_values = []
+        if os.getenv("NVIDIA_PROJECT_ID") is None:
+            default_values.append("project_id='test-project'")
+        if os.getenv("NVIDIA_DATASET_NAMESPACE") is None:
+            default_values.append("dataset_namespace='default'")
+        if os.getenv("NVIDIA_DATASETS_URL") is None:
+            default_values.append("datasets_url='http://nemo.test'")
+
+        if default_values:
+            warnings.warn(
+                f"Using default values: {', '.join(default_values)}. \
+                          Please set the environment variables to avoid this default behavior.",
+                stacklevel=2,
+            )
+
+    @classmethod
+    def sample_run_config(cls, **kwargs) -> Dict[str, Any]:
+        return {
+            "api_key": "${env.NVIDIA_API_KEY:}",
+            "dataset_namespace": "${env.NVIDIA_DATASET_NAMESPACE:default}",
+            "project_id": "${env.NVIDIA_PROJECT_ID:test-project}",
+            "datasets_url": "${env.NVIDIA_DATASETS_URL:http://nemo.test}",
+        }