feat: support proxy routing via gRPC default_authority

[raflFaisal]

This PR

To provide a :authority header to request route to target backend services using default_authority parameter by the JS clients. This enable better integration with service proxies like Envoy, facilitating more flexible and robust gRPC client configurations.

Related Issues

#1187
open-feature/flagd#1532

How to test

Use defaultAuthority parameter to pass down the target authority when sending a grpc request from client side.

[toddbaert]

I'm OK with this solution, but it's distinctly different from the solution in other providers as you noted here:

Unfortunately, for Node.js, such support for Custom Name Resolution is not available.

While I'm OK with this solution, the title of this PR (which is what will show up in the release notes) doesn't seem accurate. It can address a subset of the same problems of a custom name resolver, but unless I'm very confused, it's not a custom name resolver.

[raflFaisal]

@toddbaert You are correct, let me change the PR title that matches with the code change.

"feat: support proxy routing via gRPC default_authority"

Let me know if it looks good to you

[toddbaert]

@toddbaert You are correct, let me change the PR title that matches with the code change.

"feat: support proxy routing via gRPC default_authority"

Let me know if it looks good to you

Yep, that sounds good to me. Just make sure to update any readme or inline docs as well to say the same sort of thing.

[toddbaert]

Approved with one minor nit here: https://github.com/open-feature/js-sdk-contrib/pull/1202/files#r1945277742

Looks really good overall. Thanks for the good README and explanations!

[beeme1mr]

I'll merge and release tomorrow. Please consider Todd's comment but I don't think it's a blocker.