Allow to configure QPS & Burst of kubernetes client

[vflaux]

Proposal

Allow to override defaults kubernetes client QPS & Burst options, like we can do with KEDA metrics apiserver.

Use-Case

We have a cluster with ~1600 ScaledObjects and we encounter heavy client-side throttling (more than a minute).
ScaledObjects takes minutes (or hours?) to be reconciled by the manager (a new ScaledObject was still not reconciled after 45min).

Anything else?

I've build an image with new flags to configure these options. We tested with QPS=100 & Burst=150 (max reconciles = 20) and we no longer have the issue. We still have some client-side throttling but they do not exceed 2s and only during the first minutes on startup.