migrate usage of merge to MergeBuckets for static analysis

[logicalhan]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

This centralizes the logic for merging buckets into component-base so that we can reliably perform static analysis on metrics that do this.

Does this PR introduce a user-facing change?

NONE

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[liggitt]

/approve
/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: liggitt, logicalhan

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