Investigate making the stackable k8s client "injectable"

[razvan]

The problem

Currently the stackable k8s client is a hard-coded struct in the operator state. Problems:

• Large portions of operator code are not unit testable.
• Related maybe Consider giving client a configurable timeout value #147
• Cannot have a synchronous client if necessary.

Proposed solution

Notes:

• Related discussions at kube-rs level:
  • Create a mock Client for testing kube-rs/kube#429
  • Remove kube::Service kube-rs/kube#532
  • Make Client configurable with Layers kube-rs/kube#539

[lfrancke]

We should talk about whether we need the Client at all or if we can use the upstream one by now and/or move things upstream.

[lfrancke]

Not needed anymore I believe