Panic dumps should be sent in API responses

[philrz]

At the time of the filing of this issue, Zed it at commit 82ddbf2.

In different recent issues, I've observed what seems to be inconsistent behavior with sending stack dumps from panics in API responses. For instance, brimdata/zui#2620 showed an issue where the panic did come back over the API such that it was ultimately shown to the user, which is very helpful. On the other hand, #4349 is an issue where the response didn't go back over the API, resulting in the app showing no results and giving the user the impression there was no result to their query when in fact zed serve had panicked.

Is there's anything general we can do to make sure these panic dumps always end up in the log and in the API response so app users know there was a problem, we can help them debug it, etc.?