feat: Add optional system collections support

[StephenGunn]

Summary

This pull request introduces an optional --includeSystemCollections CLI flag to include Directus system collections in the generated TypeScript definitions. By default, the tool only generates types for user-defined collections discovered through spec.paths. With this new flag enabled, we also check spec.components.schemas for x-collection fields, adding those collections to the final output.

Changes

• Added a new --includeSystemCollections boolean flag (default false).
• When enabled, system collections defined in spec.components.schemas that have an x-collection property are included in the generated types.
• To prevent duplicates (where the same collection might appear both in paths and components.schemas), we now gather all collections first in a collections object and only write them out once at the end. This avoids repetitive entries without heavily modifying the existing if (spec.paths) logic, keeping the original structure intact.

Reasoning Behind the Logic Change

Initially, collections were appended directly to the output source as they were discovered. With the addition of system collections (and thus a second method of discovering them), it became possible to generate the same collection twice. To fix this without diverging too much from the original approach, I switched to a two-step process:

1. Collect all user-defined and optional system collections into a single data structure.
2. Write them out in one pass, ensuring each collection is listed only once.

This preserves most of the original logic while simply deferring when we write to source.

Testing

• Verified locally by generating types with and without the --includeSystemCollections flag.
• Confirmed that enabling the flag adds system collections and doesn’t produce duplicates.
• Confirmed that disabling the flag results in the original behavior, maintaining backward compatibility.
• Checked against a running Directus server and a directus.oas.json with identical results
• Builds with no errors or warnings.

Documentation

• Updated the README to describe the new --includeSystemCollections option and its usage.

Impact

• Minor version bump (1.1.0) since this is a backward-compatible enhancement.
• No breaking changes introduced.

Thank you for this project, hope you understand why this will help!