Outdated KubernetesServiceDiscovery lookup

[segabor]

First off, you did an amazing work! Thanks for that.

Unfortunately the project doesn't build, supposedly due to a breaking change in a dependency.

lookup method in SwiftKubeServiceDiscovery class has two problems,

1. whenComplete completion callback no longer exists. I suppose it has been superseded by async / await structure.
2. So the method itself should be transformed to an async function.

[iabudiab]

@segabor thank you for raising the issues. I must admit, that I've neglected this module and didn't update it promptly. I have, however, started a new branch with an almost complete overhaul using structured concurrency a while back but got distracted and didn't finish it.

I'll give it another go as soon as I get a couple of days with some free time 😉

[segabor]

Sounds great!