Use gitlab handle in link_to_team_member helper

Why is this change being made?

The release schedule page has some links to team members that are broken or incomplete. This is because the link helper is using the slug and this does not match what the team page uses for the anchor tag. It seems the correct property is gitlab

Does this MR meet the acceptance criteria?

Assign to DRI

• Did you assign this change to the correct DRI of the page or information you are changing?

Conformity

• Added description to this MR explaining the reasons for the proposed change, per say-why-not-just-what