dependencies search: lockfile service call should not hard fail on first error

Created by: tsenart

This query shows "No results", even though we know some of the repos (like sourcegraph/sourcegraph) definitely have dependencies. I briefly looked at a failing trace and I think the reason is we hard fail the whole thing if any (repo, rev) pair errors when calling the lockfile service on it.

https://github.com/sourcegraph/sourcegraph/blob/e3de126a593b9b52f0cdb355fcd57f8505f1dcec/internal/codeintel/dependencies/service.go#L150-L163

Instead, we should aggregate errors and convert them to a search alert, but still return results for what we can find.