docs: correct Rack Attack rate limits

[devlikepro]

Summary

Corrects the documented Rack Attack rate limits.

Why

The global IP throttle is configured from RACK_ATTACK_LIMIT with a default of 3000 over 1 minute, so the docs should not describe it as 60rpm or 60rps. Widget API throttles have separate limits and should be documented separately.

What this change does

• Documents the default IP throttle as 3000 requests per 1 minute
• Clarifies the default allowed IPs
• Adds the widget API limits controlled by ENABLE_RACK_ATTACK_WIDGET_API

Validation

• Cross-checked against config/initializers/rack_attack.rb in the Chatwoot codebase
• Ran git diff --check