Docs: Kubernetes advanced config

Why was this MR needed?

Just saw that docs/configuration/ still references deprecated configuration keyword. In addition lots of keywords are describes in "default" and "advanced" config which is not ideal and there are still references to the "you need to have git in your image" workaround. I also tried to keep the default configuration example at a minimum.

What are the relevant issue numbers?

!391 (merged), !384 (merged), !383 (merged), !425 (merged)

@tmaczukin could you please have a look? Would be cool to have this %v1.10 as well I think.