Add except-change-detector for RN/Task validation

[MichielOda]

This pull request introduces a new composite GitHub Action, exempt-change-detector, to classify PRs as "exempt" when all changed files match specific patterns (such as GitHub workflow/config or unit-test projects). It also updates the references-parser action to support an "exempt" mode, relaxing the requirement for a task id when a PR is exempt. Both actions now support improved configuration, extensibility, and test coverage.

New exempt-change-detector action:

• Action implementation and documentation:
  • Added .github/actions/exempt-change-detector/ with a full implementation (exempt-change-detector.ps1), composite action definition (action.yml), documentation (README.md), and comprehensive test script (test.ps1). The action outputs exempt=true if all changed files match configured glob patterns, otherwise false. [1] [2] [3] [4]
• Glob pattern matching:
  • Supports advanced glob patterns (*, ?, **, **/), case-insensitive matching, and default patterns for GitHub config and unit-test folders/files.
• Usage and integration:
  • Provides example usage and default patterns, enabling seamless integration in workflows that need to conditionally relax PR requirements. [1] [2]

Enhancements to references-parser action:

• Exempt mode support:
  • Added an exempt input to allow PRs classified as exempt (e.g., by the new action) to skip the task id requirement, requiring only an RN. This is reflected in both validation logic and the generated summary/comment. [1] [2] [3] [4] [5] [6] [7]
• PR body file input:
  • Added support for a pr-body-file input, allowing the action to read the PR description from a file, which is useful for workflows that fetch or auto-edit the PR body. [1] [2] [3] [4] [5] [6]
• Extended test coverage:
  • Added and updated test cases to cover exempt mode, PR body file input, and all new validation scenarios. [1] [2] [3]

These changes make it easier to automate and streamline PR validation for exempt changes, reducing manual work for configuration or test-only PRs while maintaining robust validation for all other cases.