[Feat] Add support for Flipt Client-Side evaluation model

[atmask]

Description: Flipt cloud only supports client-side evaluation models. Self-hosted flipt instances support both. To provider a wider coverage of open-feature for end-users there should be support for both evaluation models.

Currently the flipt provider wraps the ofrep provider which is fine for evaluation against a self-hosted instance, however, this implementation will need to wrap the official client side sdk: https://github.com/flipt-io/flipt-client-sdks/tree/main/flipt-client-python

@markphelps tagging you for visibility

[atmask]

I'll start working on adding the support for this. Should be done in not too long. I just started tonight. It will new python provider: openfeature-provider-flipt-client

[atmask]

MR wth the implementation for this is available but I still need to come back and write all of the unit tests: #179

I have explained implementation details in the PR and modelled it closely on the OpenFeature JS/Web Flipt Client provider.

@beeme1mr @markphelps I would appreciate a pair of eyes on the PR while I start adding the tests so that I can adapt any of the implementation if needed before enforcing it with the tests. Thanks!