metricServer can set readOnlyRootFilesystem=true

[joebowbeer]

The keda README in this repo states that metricServer cannot set readOnlyRootFilesystem=true

Metrics server needs to write the self-signed cert so it's not possible set this
readOnlyRootFilesystem: true

but the FAQ says otherwise and provides instructions how to do it when using the default generated cert:

Originally posted by @joebowbeer in #267 (comment)

    readOnlyRootFilesystem: true
  volumes:
    metricsApiServer:
      extraVolumes:
      - name: keda-volume
      extraVolumeMounts:
      - name: keda-volume
        mountPath: /apiserver.local.config/certificates/

Please add this secure snippet to the secure-by-default values, or add a reference to the FAQ in the comment.

[JorTurFer]

@kedacore/keda-helm-maintainers ?

[tomkerkhove]

We can do it, but there seem to be some pre-requisites. I'd leave it up to @zroubalik as I'm not familiar with this enough

[joebowbeer]

I'm just pointing out that this section of the README is contradicted by the FAQ, and I'm suggesting ways to bring it into line, including a snippet for values that works with the default generated cert.

My PR that updated the FAQ is kedacore/keda-docs#830