feat(ofrep): http handler implementation

[ZackarySantana]

This PR

• adds an ofrep handler

After starting to adopt an ofrep client, I was surprised there's no minimal http handler wrapper around a go openfeature provider already. This PR adds a very bare bone one. This is my first time contributing to this repo, so feel free to critique it!

How to test

• adds unit tests for default configuration and with options

[thomaspoignant]

Hey @ZackarySantana I am not sure to understand what is the goal of this HTTP Handler.
Can you tell me a bit more about this?

GO has already an OFREP provider https://github.com/open-feature/go-sdk-contrib/tree/main/providers/ofrep, and I am not sure to understand what this is bringing around OFREP.

[ZackarySantana]

Hey @thomaspoignant, this adds a server-side http handler wrapper so a go provider can be exposed over OFREP and then accessed by other clients. For example a provider written in go can be exposed with this handler and then consumed from the javascript ofrep provider (or another go ofrep provider, in a microservice architecture).

[ZackarySantana]

I expose it as a handler and leave serving it to the consumer, so they can add authentication and etc.