Add a WatchStreamExt::modify shortcut

[clux]

Would you like to work on this feature?

no

What problem are you trying to solve?

Minor ergonomics improvement for the streams api. Currently stream modification requires:

let stream = watcher(api, watcher::Config::default()).map_ok(|ev| {
    ev.modify(|pod| {
        pod.managed_fields_mut().clear();
        pod.annotations_mut().clear();
        pod.status = None;
    })
});

we could shortcut that ever so slightly:

let stream = watcher(api, watcher::Config::default()).modify(|pod| {
    pod.managed_fields_mut().clear();
    pod.annotations_mut().clear();
    pod.status = None;
});

Describe the solution you'd like

A new WatchStreamExt::modify that chains TryStreamExt::map_ok with watcher::Event::modify

Can be verified in examples/pod_reflector.rs.

Describe alternatives you've considered

writing out the full thing, not a big deal, but a nice user facing api simplification when using the streams api.

Documentation, Adoption, Migration Strategy

additive change, put it in the docs and the example.

Target crate for feature

kube-runtime

[nightkr]

Yeah, nested maps tend to feel pretty awkward, especially when this is something that we want to encourage.