Make clone repo more explicit in executor job payload

Created by: eseliger

We want to signify more clearly that a repo needs to be cloned/doesn't need to be cloned in the job payloads. Currently, code intel jobs set these values while for batch changes we omit them, which implicitly means "don't fetch the repo".

A bonus could be to use the "standard" executor fetching in src exec as well, so it doesn't have to download the archive later. This would likely need to support zips though because we want to be able to have only subtrees downloaded. The benefit of this would be that we don't need to use user auth tokens at all at some point then. The task will be given to the exec command, the cache entries will be passed in locally, changeset_specs will be created server-side. This should remove all requests where we reach out to Sourcegraph directly. One step toward getting rid of user tokens exposed inside the firecracker VMs.