Add support for nacos for service discovery

[zhiqiangxu]

Nacos is primarily used for service discovery in microservices(most popular in the Java ecosystem), and it would be beneficial for Kong to support it.

[chronolaw]

I think that currently kong does not support nacos and has no plan for it. There is a blog that may be useful: https://konghq.com/blog/learning-center/service-discovery-in-a-microservices-architecture.