Add documentation for outputs and artifacts in psake

This addresses a common question about how to return data from psake
scripts, such as artifact URLs or build metadata. The new documentation
covers:

- Script-level variables for simple data
- Output files (JSON/YAML) for CI/CD integration
- Environment variables for pipeline integration
- BuildTearDown for centralized reporting
- Anti-patterns to avoid
- Complete working examples

The documentation is added to the Tutorial - Advanced section as it
covers patterns for working with build outputs and artifacts.

Author: claude