Add Organization Feature Flags & Vault Support

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Description

Added Organization Feature Flags functionality in Organizations by introducing the getFeatureFlags($organizationId) method. Added tests to validate organization feature flags.

Resolved a deprecated notice in the OrganizationsTest to ensure compatibility with newer PHP versions.

Implemented support for reading Vault items.

Expanded the test suite to encompass Vault-related functionalities.

Documentation

This may allow a change to docs, however I do not believe I have access to that repository.

Does this require changes to the WorkOS Docs? E.g. the API Reference or code snippets need updates.

[ ] Yes

If yes, link a related docs PR and add a docs maintainer as a reviewer. Their approval is required.