feat: Add Flipt provider

[atmask]

Overview

This PR implements the Flipt provider by wrapping around the OFREP Provider and leveraging Flipt's OFREP api

Discussion Points:

• Should we support passing the namespace in the constructor this way or just leave it up to users to do it themselves via the generic headers_factory (like they would need to for authentication)

Related Issues

Fixes #89

How to test

Unit Tests: From the base of the package run hatch test

Local Usage: Go to the base of the new packager (i.e. provider/openfeature-provider-flipt), run pip install -e ., and then open a python repl with python3:

from openfeature import api
from openfeature.contrib.provider.flipt import FliptProvider
api.set_provider(FliptProvider(base_url="<flipt instance>", namespace="<your namespace>"))
client = api.get_client()
client.get_boolean_value("<your feature flag key>", True)

[markphelps]

lgtm! just curious if this gives end users much over the generic Python OFREP impl? Is the end goal of OFREP to make it easier to implement provider specific sdks or to be 'the' SDK for all providers that support it?

cc @beeme1mr

[atmask]

Something we might want to consider is that this will result in the output of the user's header's factory being called once and the output being merged into the dict here. That dict will always be returned without the user's header's factory being called again. This could be fine it you are okay with it but it is a change from the current implementation where the user's headers_factory is called on every feature flag evaluation in the OFREP provider.

I think I could turn this into a closure around the user's headers_factory callable if that is something we might be concerned about.