Fix Configure team page not displaying team members

Why is this change being made?

https://about.gitlab.com/handbook/engineering/development/ops/configure/#team-members is empty and all team members are shown in the table below (stable counterparts). This is because Nicholas has two roles in his "person" file and the code, that renders the page is not robust enough to handle this.

This MR fixes the issue by using manager's slug instead of role to find team members.

Author Checklist

• Provided a concise title for the MR
• Added a description to this MR explaining the reasons for the proposed change, per say-why-not-just-what
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  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to one of the people listed in the "Maintained by" section in on the page being edited.
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• If the changes affect team members, or warrant an announcement in another way, please consider posting an update in #whats-happening-at-gitlab linking to this MR.
  • If this is a change that directly impacts the majority of global team members, it should be a candidate for #company-fyi. Please work with internal communications and check the handbook for examples.

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