feat: added nvidia as safety provider

[cdgamarose-nv]

What does this PR do?

Adds nvidia as a safety provider by interfacing with the nemo guardrails microservice.
This enables checking user’s input or the LLM’s output against input and output guardrails by using the /v1/guardrails/checks endpoint of the guardrails API.

Test Plan

Deploy nemo guardrails service following the documentation: https://developer.nvidia.com/docs/nemo-microservices/guardrails/source/getting-started/deploy-docker.html

Standalone:

(venv) local-cdgamarose@a1u1g-rome-0153:~/llama-stack$ pytest -v -s llama_stack/providers/tests/safety/test_safety.py --providers inference=nvidia,safety=nvidia --safety-shield meta/llama-3.1-8b-instruct

=================================================================================== test session starts ===================================================================================
platform linux -- Python 3.10.12, pytest-8.3.4, pluggy-1.5.0 -- /localhome/local-cdgamarose/llama-stack/venv/bin/python3
cachedir: .pytest_cache
metadata: {'Python': '3.10.12', 'Platform': 'Linux-5.15.0-122-generic-x86_64-with-glibc2.35', 'Packages': {'pytest': '8.3.4', 'pluggy': '1.5.0'}, 'Plugins': {'metadata': '3.1.1', 'asyncio': '0.25.3', 'anyio': '4.8.0', 'html': '4.1.1'}}
rootdir: /localhome/local-cdgamarose/llama-stack
configfile: pyproject.toml
plugins: metadata-3.1.1, asyncio-0.25.3, anyio-4.8.0, html-4.1.1
asyncio: mode=strict, asyncio_default_fixture_loop_scope=None
collected 2 items

llama_stack/providers/tests/safety/test_safety.py::TestSafety::test_shield_list[--inference=nvidia:safety=nvidia] Initializing NVIDIASafetyAdapter(http://0.0.0.0:7331)...
PASSED
llama_stack/providers/tests/safety/test_safety.py::TestSafety::test_run_shield[--inference=nvidia:safety=nvidia] PASSED

============================================================================== 2 passed, 2 warnings in 4.78s ==============================================================================

Distribution:

llama stack run llama_stack/templates/nvidia/run-with-safety.yaml
curl -v -X 'POST' "http://localhost:8321/v1/safety/run-shield" -H 'accept: application/json' -H 'Content-Type: application/json' -d '{"shield_id": "meta/llama-3.1-8b-instruct", "messages":[{"role": "user", "content": "you are stupid"}]}'
{"violation":{"violation_level":"error","user_message":"Sorry I cannot do this.","metadata":{"self check input":{"status":"blocked"}}}}