import: want better errors than context canceled

[andreimatei]

When an IMPORT statement fails for whatever reason, we seem to commonly only get a communication error: rpc error: code = Canceled desc = context canceled error as a result of that query.
Examples just from today:
#38131 (comment)
#38136 (comment)

That error is useless. It comes from the DistSQL inbound stream processor which is interrupted by the ctx cancelation.
One way or another, we should try to get our hands on the error that caused this cancelation. Perhaps the situation will improve with @jordanlewis's work on providing causes for the cancelation, but I'm not too hopeful in this case since here the original error is probably very far removed from this cancelation - probably on another node, and gRPC is probably involved in canceling some contexts (in fact I'm not sure how this ctx canceled error even makes its way back to the gateway).
What seems to me like a promising direction is trying to add smarts at the DistSQLReceiver level or above for prioritizing some errors over other when a query receives multiple errors - and in particular de-prioritizing the context canceled errors.

@dt do you want this one?

Jira issue: CRDB-5644

[github-actions]

We have marked this issue as stale because it has been inactive for
18 months. If this issue is still relevant, removing the stale label
or adding a comment will keep it active. Otherwise, we'll close it in
10 days to keep the issue queue tidy. Thank you for your contribution
to CockroachDB!