[RFC] Adaptive automatic flow control

## Issue Description

Type: *feature request*

### Describe what feature you want

It would be perfect if we can introduce intelligent mechanisms that do adaptive flow control automatically based on real-time metrics. Thus the services can react to burst traffic timely and become more resilient. Users might not need to configure rules anymore.

No files, tests, or entry points are named in the issue. Start by reviewing Sentinel's existing flow-control and monitoring components, then define how real-time metrics should drive automatic adaptation and how burst-traffic resilience would be verified without user-configured rules.

Written by the indexing model from the issue text.