OpenAI skill trigger/Return value from pipeline

[andystaples]

Return a value for assistantSkillTrigger similar to Durable Activities

resolves #issue_for_this_pr

Pull request checklist

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

[andystaples]

TODO: Discuss documentation, release notes, potential side-effects, parity w/ other ooproc langs

[AnatoliB]

Not right now, but if we need to make changes in this area in the future (perhaps adding yet another exception for other triggers): we should probably extract all the places controlling the return value and tracing behavior to a separate class, so we don't have to search for these places again and can just add one more trigger to the list. LGTM for now though.