feat(flags): Support /decide?v=4 and include version info flag called events (#1837)

* Support `/decide?v=4`

This also includes the feature flag `version` and the evaluation `reason` in the `$feature_flag_called` event.

This is done in a backwards compatible manner so if it's pointing at `/decide?v=3`, it will still work fine, it'll just lack the version info.

This depends on:  PostHog/posthog#29751

* Add support for overrides

* And include original values in the  event

* Update src/__tests__/featureflags.test.ts

Co-authored-by: greptile-apps[bot] <165735046+greptile-apps[bot]@users.noreply.github.com>

* Fix tests

* Fix docs for overrideFeatureFlags.

* Don't send flag details with every capture

It's a lot of data to send with every single capture.

* Include the entire reason in the event

* Include version if it's not undefined

* Use the description in the event properties

* Make sure `originalDetail` is not null.

Co-authored-by: greptile-apps[bot] <165735046+greptile-apps[bot]@users.noreply.github.com>

* Make library still request `/decide?v=3`

Since it's back compatible, let's keep requesting v3 and make sure it works.

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Co-authored-by: Dylan Martin <[email protected]>
Co-authored-by: greptile-apps[bot] <165735046+greptile-apps[bot]@users.noreply.github.com>

Author: 3 people