Better message for memory limit errors

[stsewd]

Details

In some cases the build fails due to memory limits, but there isn't a clear message of what happened (I think I see some few projects with the correct message, or maybe none?).

See #3031, #3603, #3612, #3580

Expected Result

A message about memory limit is shown.

Actual Result

A plain message "Build failed" is shown.

I'm not sure if we can catch this types of errors on the environment.

[humitos]

We have some code written to try to catch this at

https://github.com/rtfd/readthedocs.org/blob/78b5781ad071de656451a262d39458c612c45be0/readthedocs/doc_builder/environments.py#L245-L253

but the problem is that even on a memory limit reached sometimes that exit code is not properly returned and some random things happened. Actually, I think that I added that look for killed in the output because of this issue.

Due those random situations is that we don't have a good solution yet.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[humitos]

I think we can close this issue for now since there is not much else we can do to catch when a memory limit was reached.

If we have a plan to reach this goal, we should write it down here and re-open the issue.