Split up team.yml

This MR splits up the team.yml file, replacing it with one file per team member.

The team.yml file remains a part of our codebase, but it is now a generated artifact.

This modifies a CI job so that it fails if the team.yml database is inconsistent with the data/team/ files.

This commits the result of running first build:split_team and then build:team_yml, first generating the set of individual files, and then ensuring that the team.yml file has the new header.

See: !73086 (merged)

Related issue: #10507 (closed)

Implementation Plan:

Since this merging this change will cause updates to the team.yml file to become build failures once it is merged, we need to minimise the time between generating the split, and merging it. Therefore this will require a review (I nominate you @vyaklushin), and once everyone is happy we need to schedule a merge window when things will be relatively quiet).

Once the merge window is decided, we need to re-generate the split, and merge this MR as quickly as possible. If possible, stopping in-flight MRs that change the team would be a very good idea.