Convert template helpers to take slugs instead of regex values
Problem statement
A recent update to team member roles caused a lot of team pages to be broken due to the following helpers looking for roles using a regex pattern rather than the team member's slug:
<%= direct_team(manager_role: 'regex here') %>
<%= stable_counterparts(direct_manager_role: 'regex here') %>
Proposed solution
It would be better for these template helpers to take a team.yml slug than a regex pattern, and to fail the build if the slug is invalid.