Replace k8s.io/client-go/scale with controller-runtime client

[zroubalik]

Proposal

controller-runtime client will soon support accessing /scale subresource:
kubernetes-sigs/controller-runtime#2094
kubernetes-sigs/controller-runtime#172

Once a version of controller-runtime with this change is released we should use it and consolidate our codebase ->
replace k8s.io/client-go/scale with controller-runtime client.

It is in the ScaledObject controller and scale executor:

keda/controllers/keda/scaledobject_controller.go

Line 67 in f4bee67

ScaleClient scale.ScalesGetter

keda/pkg/scaling/executor/scale_executor.go

Line 47 in f4bee67

scaleClient scale.ScalesGetter

[dttung2905]

This MR above has been included in 0.14.0 of the sigs.k8s.io/controller-runtime (Changelog).
Can I take up this task, if you don't mind ? I'm reading up on the documentation for controller-runtime to catch up on the missing knowledge but will definitely need your help/guidance along the way

[zroubalik]

@dttung2905 great, thanks!

[dttung2905]

Update: It is needed to update thepredictkube-libs as well. It uses older version of k8s.io/client-go which has breaking changes in the latest version
PR: dysnix/predictkube-libs#7

[zroubalik]

@dttung2905 thanks for the heads up!