feat(ado-gha-axe-core): remove check run, add workflow enforcer, add fail-on-accessibility-error

[brocktaylor7]

Details

This PR:

1. Removes the check run in preparation to remove the repo-token in a future PR.
2. Adds a GHWorkflowEnforcer progress reporter that operates the same way the newly renamed AdoWorkflowEnforcer already works. Its job is to run last and fail the build if anything has failed along the way. This decouples failing the build from the logic of the other individual progress reporters, so that each of them can run without the build failing, which would abort the remaining tasks.
3. Adds a fail-on-accessibility-error input that defaults to true. This is also bringing the GH Action to parity with the ADO Extension. Without the check run, there was no way to not fail the build if there were accessibility issues. Where we don't have baselining yet on the GH action, this allows people to not fail the build when errors are found.
4. Updates the self-test.yml to use node16.

Here are two test runs from my test action:

• fail-on-accessibility-error not set (defaults to true)
  • https://github.com/brocktaylor7/accessibility-insights-action-test/runs/7081340086?check_suite_focus=true
• fail-on-accessibility-error set to false:
  • https://github.com/brocktaylor7/accessibility-insights-action-test/runs/7081357518?check_suite_focus=true

Motivation

Feature work

Context

The repo-token input will be removed in a future PR.

Impact for ADO Extension: This renames the WorkflowEnforcer class in the ADO Extension to more easily distinguish it from the new GHWorkflowEnforcer, but does not change any functionality.

Pull request checklist

• [n/a] Addresses an existing issue: Fixes #0000
• Added relevant unit test for your changes. (yarn test)
• Verified code coverage for the changes made. Check coverage report at: <rootDir>/test-results/unit/coverage
• Ran precheckin (yarn precheckin)
• Described how this PR impacts both the ADO extension and the GitHub action