Add CrowdSec IP reputation documentation

[lixmal]

Describe your changes

Add documentation for the CrowdSec IP reputation feature across the reverse proxy docs and self-hosted guides.

• Document CrowdSec modes (off/enforce/observe), decision types, and restriction evaluation order in the authentication and access restrictions page
• Add CrowdSec deny reasons and observe-mode behavior to the access logs page
• Update the reverse proxy overview to mention CrowdSec alongside CIDR and country restrictions
• Add Step 7 (optional) to the Enable Reverse Proxy migration guide with full CrowdSec container setup, bouncer registration, env vars, and troubleshooting
• Add CrowdSec pointer page under self-hosted maintenance with nav entry
• Mention CrowdSec in the self-hosted quickstart guide

Related PRs:

• [management, proxy] Add CrowdSec IP reputation integration for reverse proxy netbird#5722 (proxy integration)
• Add CrowdSec IP reputation dashboard#600 (dashboard UI)

Screenshots