To distinguish between working-copy-to-storage (local) and
storage-to-storage (remote) replication, we create two new
URL types: a `remote::Url` (`heartwood://`) and a `local::Url`
(`rad://`).
These schemes are to be used for the remote and local transports,
respectively.
The difference between the two schemes is that remote replication
requires a node id.
Signed-off-by: Alexis Sellier <alexis@radicle.xyz>