Add secure connection support for FlagD provider

[josecolella]

What?

This issue is to track what it would take to add secure connection to the flagd provider

Reference 📜

https://github.com/open-feature/ruby-sdk-contrib/pull/2/files#r1061691267

[josecolella]

https://github.com/tnir/gitlabhq/blob/f825fd1d881ce077ad868a70fd8d7db6a49e4700/lib/gitlab/gitaly_client.rb#L66

[josecolella]

@toddbaert I was looking at the grpc code and there seems to be several options for secure connection:

See the following:
https://github.com/grpc/grpc/blob/06a9fbd3822e33e30fb62c5fc201f13886ede3f4/src/ruby/end2end/grpc_class_init_client.rb#L82

I noticed in the js implementation there is a helper for creating a secure connection: https://github.com/open-feature/js-sdk-contrib/blob/main/libs/providers/flagd/src/lib/service/grpc/service.ts#L37

I'm confused which we would opt for in the ruby version

[toddbaert]

I'm confused which we would opt for in the ruby version

I'll try to wrap my head around this and consider it when I review your PR.

[josecolella]

@toddbaert I think I figured it out, one of the things that's interesting is that the js implementation doesn't seem to reference any root cert but you are just calling the createSsl method.

[josecolella]

@toddbaert is you see the ruby implementation, I create a ChannelCredentials that takes in three arguments; the root cert, the client pem and client .key. Looking at the tests for the secure credentials, it seems we only really need the root cert. https://github.com/open-feature/ruby-sdk-contrib/pull/8/files#diff-107800d1f2e81e1a1cee625510ebc053f2d8e366b44610db6a7b8078807fcd0cR83-R85