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

docs/source/distributions/self_hosted_distro/nvidia.md

@@ -6,7 +6,7 @@ The `llamastack/distribution-nvidia` distribution consists of the following prov
 | API | Provider(s) |
 |-----|-------------|
 | agents | `inline::meta-reference` |
-| datasetio | `inline::localfs` |
+| datasetio | `inline::localfs`, `remote::nvidia` |
 | eval | `remote::nvidia` |
 | inference | `remote::nvidia` |
 | post_training | `remote::nvidia` |