Build average location factor charts from team.yml

Why To maintain financial efficiency (and also a form of diversity) we like to hire all over the globe, and target efficient geographies. We don't currently surface the average rent index of their teams to managers, making it difficult for hiring managers and recruiting to manage this effectively.

Steps

1. Add rent_index: 0.5 to team.yml as an optional parameter.
2. Create a template helper to embed average rent index history and current state

• Similar to the hiring charts: https://about.gitlab.com/handbook/hiring/charts/quality-department/

1. Facet by the values in the departments: property array

Disadvantages/mitigations

• You can potentially derive someone's salary using rent index and the calculator
  • Mitigation: Location is already present in team.yml (and easily found online, otherwise) and it's a short hop from there to rent index anyway
  • Mitigation: You actually can't, because experience factor is a necessary but confidential input into the calculator

CC @sytses