Consul NameService supports dc

**Is your feature request related to a problem? (你需要的功能是否与某个问题有关?)**
consul服务发现不支持跨dc

**Describe the solution you'd like (描述你期望的解决方法)**
consul服务发现uri支持可选的dc参数，例如：
consul://some.service.name(@dc)

**Describe alternatives you've considered (描述你想到的折衷方案)**
复制其它dc的服务到local dc（目前consul replicate也不支持，只能自己写脚本？）

**Additional context/screenshots (更多上下文/截图)**

Start by locating the Consul NameService implementation and the URI parsing entry point for service names. Trace how service discovery selects a datacenter, then define coverage for an optional dc parameter such as consul://some.service.name(@dc). Done means cross-datacenter lookup works and the behavior is covered by tests.

Written by the indexing model from the issue text.