Update OWNERS

[mmerkes]

Add mmerkes as an approver

What type of PR is this?
/kind cleanup

What this PR does / why we need it:
I've been an active reviewer on this repo for a while and want to help maintain it.

Which issue(s) this PR fixes:
N/A

Special notes for your reviewer:
N/A

Does this PR introduce a user-facing change?:

NONE

[k8s-ci-robot]

This issue is currently awaiting triage.

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[dims]

/approve

leaving /lgtm for another approver

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dims

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [dims]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[cartermckinnon]

/lgtm