Add "transaction" or "trace" ID to HTTPError class

As a service operator, I would like to give the user an ID they can provide to me while troubleshooting an issue, so that I can quickly find any relevant events in my logs.

Start by locating the HTTPError class and any tests covering its construction and response output. Review how request errors are logged and decide how the proposed transaction or trace ID should reach users and correlate with logs; done means the behavior is covered by tests and the ID is available during troubleshooting.

Written by the indexing model from the issue text.