mod_http_oauth2: Record details of OAuth client a token is issued to To enable use cases such as revoking all tokens issued to a particular OAuth client in case of security issues, or for informative purposes such as when listing tokens for users.

This module writes out a traceback to `traceback.txt` in Prosodys data
directory (see `prosodyctl about`) when the signal `SIGUSR1` is
received. This is useful when debugging seemingly frozen instances in
case it is stuck in Lua code.