fix: serve 404 if ctx is canceled while resolving a domain

What does this MR do?

If the ctx is canceled while resolving a domain we should serve a 404 (this is consistent with other context.Canceled handling).

Note: TestSlowRequest is not able to catch this because it succeed thanks to the 404 returned by the ping request (see func WaitUntilRequestSucceed).

TODO

• I added the Changelog trailer (e.g. Changelog: added) to the commits that need to be included in the changelog
• I added unit tests or they are not required
• I added acceptance tests or they are not required
• I added documentation (or it's not required)
• I followed code review guidelines
• I followed Go Style guidelines