Add feature flags to parsed access-token results (#1295)

## Description
This change pulls the `feature_flags` claim from the JWT if it exists.
This claim is exposed as `featureFlags` to the developer.

## Documentation

Does this require changes to the WorkOS Docs? E.g. the [API
Reference](https://workos.com/docs/reference) or code snippets need
updates.

```
[X] Yes - https://github.com/workos/workos/pull/40562
```