Add *teams* sync to the mergebot

Currently the mergebot is able to sync employees in order to auto-provision their account & give them backend access.

In order to better classify users (mostly in the context of forward ports) teams were created (as companies), however assignment of employees to those teams / companies has been extremely ad-hoc and I've no really kept up with it.

It would be nice to have accounts automatically push this information to the mergebot, alongside changes in employees (as in, an employee changing team). Although it's not necessarily a super important thing as we can reasonably easily massage import / export features into doing that...

Also would probably make sense to store the reviewer's team on the PR at review (also author's?) such that the PR is then associated specifically with a review team, and the forward ports can more easily be reassigned if the employee changes team or leaves.

No files or tests are named. Start by tracing the existing mergebot employee synchronization and the import/export paths mentioned in the issue, then map how teams and pull-request reviews are represented. Done should include automatic team assignment updates and a defined association between reviewers or authors and the team on each pull request.