Support custom name resolution in flagd providers

[beeme1mr]

Summary

Introduce support for custom name resolution in flagd providers to enable better integration with service proxies like Envoy, facilitating more flexible and robust gRPC client configurations.

Background

In distributed systems, service proxies like Envoy are often used to manage traffic routing, load balancing, and observability. These proxies rely on the :authority header to route requests to the appropriate backend services. Some languages expose a mechanize for easily adding Custom Name Resolver (see gRPC docs), while others must be manually configured.

Requirements

Tasks

Preview Give feedback

1. docs: added gRPC custom name resolver proposal #1414
   size:L +1
2. Include custom name resolution RFC in docs
3. feat: added custom grpc resolver #1424
   size:L +1
4. feat: added custom grpc resolver go-sdk-contrib#587
   +0
   

   
5. [flagd] Support custom schemes (name resolvers) java-sdk-contrib#995
   +0
   
6. [flagd] Support custom schemes (name resolvers) js-sdk-contrib#1187
   +0
   
7. Custom gRPC resolver in Python
8. Custom gRPC resolver in .NET

References

• gRPC Custom Name Resolve Spec
• Custom gRPC resolver E2E implementation