chore(helm): Add location to set hostUsers

[jcpunk]

What this PR does / why we need it:

Currently there is no place in helm to note if you want to try this out using user namespaces. This PR adds a flag where folks can start to experiment with user namespaces and metrics-server.

This defaults to the current kubernetes default and omits the flag on versions which may not have the feature.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: jcpunk
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[k8s-ci-robot]

This issue is currently awaiting triage.

If metrics-server contributors determine this is a relevant issue, they will accept it by applying the triage/accepted label and provide further guidance.

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[k8s-ci-robot]

Hi @jcpunk. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[stevehipwell]

@jcpunk have you opened an issue to discuss the viability of this?

CC @serathius

[jcpunk]

I don't have an issue open. I figured setting it to true which is the current default would be in effect a no op. Last I knew hostUsers: false was an alpha feature, so I'm not sure if it has even been tested with metrics-server.