docs: add guicassolato as gwctl reviewer

[shaneutt]

What type of PR is this?

/kind documentation

What this PR does / why we need it:

@guicassolato has been working diligently on Policy Attachment and Metaresources as part of the Kuadrant project. That project is heavily invested in Policy Attachment, and as such gwctl is important to them. He has agreed to help out with some of the review for gwctl going forward, which is greatly appreciated! Thank you @guicassolato!

[k8s-ci-robot]

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[shaneutt]

Need to resolve the org membership stuff first then will re-open

[guicassolato]

Thanks, @shaneutt. Request sent: kubernetes/org#5118

[mlavacca]

Thanks, @guicassolato!

/approve
/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: mlavacca, shaneutt

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