[OFREP] create the initial version of the remote evaluation protocl

[Kavindu-Dodan]

Background

With the merging of open-feature/protocol#2, we have the first version of OFREP ready. And there are already efforts ongoing to implement flag management system support for the OFREP [1]

Goal

As a contributor and maintainer of the OF Go SDK, I would like to have the first version of the OFREP provider in Go SDK.

For the first implementation, consider the following,

• Only rely on single flag evaluations as Go SDK works with the dynamic context paradigm
• Use well-known, well-established libraries where needed
• No caching in the initial version (keep it simple)
• Include a documentation and a usage guide

AC

The first version of the OFREP Go SDK is ready

[1] - open-feature/flagd#1245