This means we no longer have to individually hard-code the `kops set`
fields, however we use the "language" we're now demonstrated.
We add tests to ensure we have parity with our existing (hard-coded)
setter logic.
Mentioned in #6942
This change allows using the --config flag and a generated configfile to set
options that were not previously supported and the use via flags is deprecated.
(https://kubernetes.io/docs/reference/command-line-tools-reference/kube-scheduler/)
I thought that it might be better to have them in a config file to ensure
support in newer kubernetes versions.
It also makes it easy to add more.