Implement owner subcommand

[popzxc]

cargo owner, but for workspaces.
The implementation is straightforward, it simply executes cargo owner for each package.

Initially, I've added a test for cargo ws owner --list, but turns out that any cargo owner command requires a token to be present (see this workflow failure), so I removed it.

[pksunkara]

Can this be done with cargo ws exec instead? What's the need for new command?

[popzxc]

Oh, I totally missed it. Yes, I think it can be done via cargo ws exec.
cargo ws owner may be a bit more intuitive/convenient, but I'm not sure if the benefits here outweigh the maintenance cost.
Feel free to close this PR if you don't think this functionality is needed.

[pksunkara]

If the benefits here outweigh the maintenance cost.

I don't think they do. Appreciate the proposal though.