doc: update structure

[miyoungc]

Please also confirm the following

• I have searched the main issue tracker of NeMo Guardrails repository and believe that this is not a duplicate

Issue Kind

Improving documentation

Existing Link

https://docs.nvidia.com/nemo/guardrails/latest/index.html

Description

https://github.com/NVIDIA-NeMo/Guardrails/pull/1480/files#r2472904260

from @Pouyanpi:

I think it'd be nice that in a follow-up PR we restructure the NeMoGuard-related docs under a dedicated section and document caching support:

files to restructure:

nemoguard-contentsafety-deployment.md
nemoguard-jailbreakdetect-deployment.md
nemoguard-topiccontrol-deployment.md
current caching support:

content_safety pattern (any model or provider using this pattern should work, not limited to NIM engines)
topic_safety pattern (any model or provider using this pattern should work, not limited to NIM engines)
jailbreak_detection
Not a must-have for this PR, but would improve documentation clarity, so something like

docs/advanced
├── nemoguard-overview.md (NEW)
├── nemoguard-contentsafety-deployment.md
├── nemoguard-jailbreakdetect-deployment.md
├── nemoguard-topiccontrol-deployment.md
├── kv-cache-resuse.md
├── nemoguard-caching.md (NEW)
└── ... (other docs)