Emit AppFailure metric for permanent user code failures

[liliankasem]

Issue describing the changes in this PR

Addressing a missing permanent app failure use case; if the dotnet worker is not able to start due to a fatal user app failure, we should capture the app failure metric

Pull request checklist

• [x] My changes do not require documentation changes
  • [ ] Otherwise: Documentation issue linked to PR
• [x] My changes should not be added to the release notes for the next release
  • [ ] Otherwise: I've added my notes to release_notes.md
• [x] My changes do not need to be backported to a previous version
  • [ ] Otherwise: Backport tracked by issue/PR #issue_or_pr
• [x] My changes do not require diagnostic events changes
  • Otherwise: I have added/updated all related diagnostic events and their documentation (Documentation issue linked to PR)
• [ ] I have added all required tests (Unit tests, E2E tests)

Additional information

Additional PR information