[RoadMap] New Plannes for ShenYu 2.7.1

### Description

## Volunteer help

Dear community，

As shenyu becomes more and more popular, it accommodates diverse needs. I've proposed some of the more important features, so if you're interested, please join us!

## Next Version(2.7.1)

### Refactor Match Cache

### MCP plugins *

### Spilt Netty Thread Pool for each Selector *
1. every selector use common netty thread pool

### Refactor gray release logic
1. design selector gray logic
2. metadata usage and storage for gray
3. Upstream extension

### Refactor Selector *
1. refactor two-level cache selector
2. rafactor two-level cache rule

### Dynamic expansion and contraction bootstrap on k8s

### Verify ShenYu Bootstrap data consistency

This is a broad roadmap covering match-cache, MCP plugin, Netty thread-pool, gray-release, selector, Kubernetes scaling, and bootstrap-consistency work, but it names no files, tests, or entry points. Choose one item, locate its existing implementation, and agree on concrete design and acceptance criteria with maintainers before starting; completion should be verified against those criteria.

Written by the indexing model from the issue text.