Add vincepri to project's maintainers

[vincepri]

What this PR does / why we need it:
Add myself to the maintainer list so I can review and approve PRs.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: vincepri
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We suggest the following additional approver: karan

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[roberthbailey]

We didn't bring this up at the meeting last week, but we should establish some sort of pseudo-formal procedure for promoting folks to be maintainers. Let me know if you have any good ideas for what data we can use to be as objective as possible (something along the lines of number of lgtms on PRs that subsequently merged seems reasonable).

/cc @justinsb in case you have ideas or suggestions from your experience promoting folks to be maintainers of kops.

[roberthbailey]

Closing in favor of #670.