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.