feat: Generate feature flags from OpenAPI spec

[gjtorikian]

Description

This PR generates the feature flags category in the Node SDK from the OpenAPI spec.

It changes a few methods from positional args to more modern object args:

 ┌────────────────────┬────────────────┬─────────────────────────────┐
  │       Method       │     Before     │            After            │
  ├────────────────────┼────────────────┼─────────────────────────────┤
  │ getFeatureFlag     │ (slug: string) │ (options: { slug: string }) │
  ├────────────────────┼────────────────┼─────────────────────────────┤
  │ enableFeatureFlag  │ (slug: string) │ (options: { slug: string }) │
  ├────────────────────┼────────────────┼─────────────────────────────┤
  │ disableFeatureFlag │ (slug: string) │ (options: { slug: string }) │
  └────────────────────┴────────────────┴─────────────────────────────┘
  └────────────────────────┴────────────────────────────┘

As well:

• createdAt / updatedAt are now Date objects, not ISO strings.

Because of this, the PR should be treated as a breaking change.