feat(go-feature-flag)!: GO Feature Flag provider rebuild

[thomaspoignant]

This PR

In this PR the GO Feature Flag provider has been completely rebuilt on top of the OFREP provider.

This implementation adds a bunch of GO Feature Flag features on top of OFREP:

• ✅ Send analytics data to the relay-proxy.
• ✅ Caching (cache the previous evaluation to reduce the number of API calls).
• ✅ Polling (call an API on the relay-proxy regularly to purge the cache when a configuration change happens on the relay-proxy).
• ✅ Eventing (this version of the provider is supporting OpenFeature eventing).

⚠️ BREAKING CHANGE

This version contains breaking changes on the configuration struct:

• ⚠️ You cannot use the GO module in the provider.
  (In order to minimize the dependencies of the GO provider, we have removed the dependency to thomaspoignant/go-feature-flag, this means that you can't use the GO module with this provider anymore BUT you can now use the new provider for this feat(go-feature-flag): GO Feature Flag in process using GO module #546).
• ⚠️ In the configuration, we removed the interface HTTPClient to use directly *http.Client.
• ⚠️ To have a fully working cache, you need to have a relay-proxy v1.32.0 or more.

Related PR

Fixes #546

[mjudeikis]

Still need to read this code few times more to get my head around but looks healthy
/lgtm

[toddbaert]

Will review.

[dangra]

Wanted to point this change causes a panic under certain conditions as explained in #578 and attempted a fix in #579