add NVIDIA NIM inference adapter (#355)

# What does this PR do?

this PR adds a basic inference adapter to NVIDIA NIMs

what it does -
 - chat completion api
   - tool calls
   - streaming
   - structured output
   - logprobs
 - support hosted NIM on integrate.api.nvidia.com
 - support downloaded NIM containers

what it does not do -
 - completion api
 - embedding api
 - vision models
 - builtin tools
 - have certainty that sampling strategies are correct

## Feature/Issue validation/testing/test plan

`pytest -s -v --providers inference=nvidia
llama_stack/providers/tests/inference/ --env NVIDIA_API_KEY=...`

all tests should pass. there are pydantic v1 warnings.


## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the
other checks if that's the case).
- [x] Did you read the [contributor
guideline](https://github.com/meta-llama/llama-stack/blob/main/CONTRIBUTING.md),
      Pull Request section?
- [ ] Was this discussed/approved via a Github issue? Please add a link
      to it if that's the case.
- [ ] Did you make sure to update the documentation with your changes?
- [x] Did you write any new necessary tests?

Thanks for contributing 🎉!

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

@@ -0,0 +1,48 @@
+# 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
+from typing import Optional
+
+from llama_models.schema_utils import json_schema_type
+from pydantic import BaseModel, Field
+
+
+@json_schema_type
+class NVIDIAConfig(BaseModel):
+    """
+    Configuration for the NVIDIA NIM inference endpoint.
+
+    Attributes:
+        url (str): A base url for accessing the NVIDIA NIM, e.g. http://localhost:8000
+        api_key (str): The access key for the hosted NIM endpoints
+
+    There are two ways to access NVIDIA NIMs -
+     0. Hosted: Preview APIs hosted at https://integrate.api.nvidia.com
+     1. Self-hosted: You can run NVIDIA NIMs on your own infrastructure
+
+    By default the configuration is set to use the hosted APIs. This requires
+    an API key which can be obtained from https://ngc.nvidia.com/.
+
+    By default the configuration will attempt to read the NVIDIA_API_KEY environment
+    variable to set the api_key. Please do not put your API key in code.
+
+    If you are using a self-hosted NVIDIA NIM, you can set the url to the
+    URL of your running NVIDIA NIM and do not need to set the api_key.
+    """
+
+    url: str = Field(
+        default="https://integrate.api.nvidia.com",
+        description="A base url for accessing the NVIDIA NIM",
+    )
+    api_key: Optional[str] = Field(
+        default_factory=lambda: os.getenv("NVIDIA_API_KEY"),
+        description="The NVIDIA API key, only needed of using the hosted service",
+    )
+    timeout: int = Field(
+        default=60,
+        description="Timeout for the HTTP requests",
+    )