cpumanager: add featuregate for cpumanager alpha policy options

[ffromani]

add feature gate to enable selected users to consume cpumanager policy options of alfpha maturtiy.
Needs to be merged alongside openshift/kubernetes#2136 which enables per-option granularity

for more details: openshift/enhancements#1724

[openshift-ci]

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[openshift-ci]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: ffromani
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[openshift-ci]

@ffromani: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
ci/prow/verify	879173d	link	true	/test verify

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[ffromani]

no longer needed per discussion in openshift/enhancements#1724