Support Spring Cloud Discovery for NameResolver/NameResolverProvider

[jpbassinello]

Considering the heavy usage of Spring Cloud Discovery in cloud-native projects, it would be great to support the integration of spring-grpc and spring-cloud for NameResolver.

The solution was implemented for https://github.com/grpc-ecosystem/grpc-spring, and I believe it can be entirely reused for spring-grpc.

https://github.com/yidongnan/grpc-spring-boot-starter/tree/master/grpc-client-spring-boot-autoconfigure/src/main/java/net/devh/boot/grpc/client/nameresolver

[spencergibb]

The way, the spring portfolio is structured, spring-grpc will not be able to have spring cloud as a dependency since for boot 4.1, the auto-configuration will move to boot and boot will depend on spring-grpc. This would need to live somewhere in spring cloud.