Allow `gh repo clone` to grab all upstream branches

### Describe the feature or problem you’d like to solve

I just ran `gh repo clone` on a fork I had of another project. `gh` helpfully added the upstream repo for me. Cool! However, I was only getting the default branch from upstream, not any of the others. I ended up needing to modify .git/config and change the `fetch` parameter in the `[remote "upstream"]` section from `fetch = +refs/heads/master:refs/remotes/upstream/master` to `fetch = +refs/heads/*:refs/remotes/upstream/*`.

### Proposed solution

I'd like to see a flag (or something) to allow setting the upstream repo to fetch everything.

### Additional context

It looks like the default was changed in https://github.com/cli/cli/issues/2557. I prefer the default back the other way (fetch gathers all upstream branches), but either way is fine as long as it's configurable.

Thanks!