Add LaunchDarkly (client-side JS) provider

[jakedoublev]

Add LaunchDarkly (client-side JS) provider

Reasoning

I want to add a provider which stores feature flags in LaunchDarkly via client-side JavaScript. This would be valuable because...

• LaunchDarkly/OpenFeature Provider support is currently only server-side Node.js
• the LD SDK's have some distinctions between server-side and client-side
• not every feature flag implementation of LaunchDarkly is within a server
• LaunchDarkly is growing in popularity as a flag vendor, especially as a FedRAMP-approved vendor

TODO:

• [ ] generate provider via tooling
• [] implement Provider interface
• [ ] add tests
• [ ] complete README

Keep in mind the CONTRIBUTING guidelines: https://github.com/open-feature/js-sdk-contrib/blob/main/CONTRIBUTING.md

[beeme1mr]

We're working on adding proper client-side support to OpenFeature. I would recommend waiting until that work is complete before building a LD client-side provider.

FYI @toddbaert

[sago2k8]

Just jumped into this issue, have you been using the client-side LD sdk, We use it in prod some feedback would be valuable in case you are using it @jakedoublev

[jakedoublev]

@sago2k8 We have been, with an OpenFeature provider we wrote ourselves because the LD OpenFeature contrib provider had not yet been developed, and you can actually read about our experience in a blog post I wrote about it.

[sago2k8]

Thanks @jakedoublev I checked the blog post, there are some interesting insights.

Yeap we contributed to the Open Feature Provider because we use it intensively, wanted to find some inspiration and feedback, so I can buy some time to implement improvements. It has been working for us but we had to implement some workarounds for the streaming changes for instance.