Google Drive source: add drive_id config to scope sync to a specific shared drive

[VictorMustin]

Problem

When authenticating with a Google account that has access to multiple shared drives (and My Drive), there's no way to scope the sync to a single shared drive. The only config option is include_patterns, which matches folder/file names — but shared drive names are not matchable since they're drive objects, not folders.

This means:

• Users must list every top-level folder explicitly as include patterns
• When new folders are added to the shared drive, they're silently excluded until patterns are updated
• There's no "set and forget" way to say "sync everything in this shared drive"

Proposed solution

Add an optional drive_id (or shared_drive_id) field to GoogleDriveConfig:

class GoogleDriveConfig(SourceConfig):
    drive_id: Optional[str] = Field(
        default=None,
        title="Shared Drive ID",
        description="If set, only sync files from this specific shared drive. Omit to sync all drives.",
    )
    include_patterns: list[str] = Field(...)

The plumbing already exists — generate_entities already iterates over drive_ids and passes drive_id to _generate_file_entities. This would just filter the list to a single drive before iteration.