People API: handle EXPIRED_SYNC_TOKEN error properly

The People API returns HTTP 400 with JSON message describing the error. In order to handle this, we need a bigger change to the overall error handling in KGAPI2::Job. It is now possible for each job to first try to handle the error on its own (regardless of the error type) and only fall back to the default existing error handling code if the job doesn't handle it.

(cherry picked from commit 441e1cd2)