Add flag to ignore lsif upload failures
Created by: efritz
This slack message raises a concern about upload failures when the dotcom instance is having issues. This occurs when the frontend is not reachable, or a 500-level error occurs because the precise-code-intel backend is having issues.
This PR adds a flag to print the error but exit 0 when they occur so that we do not fail open-source builds when our own service is having issues.