Scalability Improvements 5: CLI Improvements

[zaadnsu]

1. During rpkg init, there should not be a pre-validation if the package exists, it will be rejected anyways by the server. It's an unnecessary lookup.
2. During rpkg clone, there should not be a pre-validation if the package exists, it will be rejected anyways by the server. It's an unnecessary lookup.
3. During rpkg upgrade, the upstream package lookup should be filtered with fieldselectors.

CC
@kushnaidu