Review Secure scheduling process

In the ~Secure team, we (backend) are using an old-school Gantt chart to follow our progression. It helps to:

• deal with dependencies between tasks
• manage OOO
• have a finer grain than open/in dev/in review/close for issues
• spot when we're late, and take a decision before the end of the iteration
• optimize everyone's schedule.
• handle many things I probably forgot

Anyway, this Gantt chart is populated during our Evaluation meeting, where everyone was giving estimates and info about PTO. This meeting doesn't scale anymore since the recent growth of the team, it's time to iterate and find a new solution. I'm thinking of an async version in a Google doc: https://docs.google.com/spreadsheets/d/1q_PoU2Jr5-htmGfPNMUyksibCUvID0GHSu9FPi7mjLI/edit#gid=0

This issue is to discuss ways to scale that process.

/cc @gl-secure