upgrade to tower 0.5.0

violently failed ci from dependabot in https://github.com/kube-rs/kube/pull/1561

not sure if this is going to be hard or not. will have a look on the weekend to see if this worth doing before next release.

[tower 0.5.0 changes](https://github.com/tower-rs/tower/releases/tag/tower-0.5.0)