feat: Add docs subcommand for searching documentation (#11490)
## Summary
- Adds `turbo docs <query>` command to search Turborepo documentation
directly from the CLI
- Results link to versioned docs site matching the current turbo version
- Includes `--docs-version` flag for explicit version override with
minimum version validation (2.7.5+)
## Testing
```bash
turbo docs "caching"
turbo docs "task dependencies" --docs-version 2.5.7
```
