Add -skip-errors flag to src campaign apply|preview
Created by: mrnugget
This fixes https://github.com/sourcegraph/sourcegraph/issues/15790 by adding the -skip-errors
flag.
Note: I made the conscious decision to only skip "runtime errors", i.e.: we can skip the failed step execution, or we can skip the failed importing of a changeset (see "after" screenshot). That means validation errors etc. are not skipped. Because I don't think that makes sense.