v3.166.0: Use a shared workflow with org secrets (#32)
This change does two things: 1. Creates a shared workflow file that's called when changes land in `master`, when deploy has been dispatched, and during PRs, so we can actually test out changes in PRs. 2. Switches to the `AZURE_SIGNING_*` org secrets, rather than the secrets in the repo, which are more up-to-date.