Refactor Staging deployment workflow to support open source PRs (#20459)

* Add a Staging build workflow

* Remove all commented out code from build workflow

It will be handled in https://github.com/github/docs-engineering/issues/726

* Use pinned version of upload-artifact action

* Tweaks to build

* Minor deployment script refactoring

* Update the Staging deployment workflow

* Missed refactoring tweak

* Add relevant comments

* Update Heroku app naming convention for Actions deploy to include 'gha-' prefix

* Update Heroku app ConfigVars and SourceBlob for optional prebuilt app

* Remove obsolete 'dist/' dir from PR build artifact

See https://github.com/github/docs-internal/pull/20405

* Ensure a new enough version of npm is used

* Switch to creating a tarball for upload

* Remove obsolete 'layouts' dir from file list

* Ditch the verbosity for 'tar'... too many files

* Add tarball support to deploy

* Add esm workaround to deploy script

See https://github.com/actions/github-script/issues/168

* Temporarily ignore staging deploy workflow from workflow linter

* Update deployment to use a Heroku Build Source instead of a GitHub Actions Artifact

* Update undeploy workflow to use ESM workaround

See https://github.com/actions/github-script/issues/168

* Add 'esm' package to optionalDependencies to better support workaround

See https://github.com/actions/github-script/issues/168

* Add Slack notifications for workflow failures

* Wrap AppSetup polling in try-catch

* Improve dyno monitoring

* Rename 'script/deploy' to have a .js extension #esm

* Update script references to include the extension

* Use non-deprecated Sources API for Heroku

* Use normal quotes

* Stub in a step to mark deployment inactive after timing out

* Apply suggestions from code review

Co-authored-by: Rachael Sewell <rachmari@github.com>

Co-authored-by: Rachael Sewell <rachmari@github.com>

tests/meta/repository-references.js

@@ -69,7 +69,7 @@ describe('check if a GitHub-owned private repository is referenced', () => {
       '**/*.pdf',
       '**/*.ico',
       '**/*.woff',
-      'script/deploy',
+      'script/deploy.js',
       'script/README.md',
     ],
   })