import post_request_task earlier so that it catches the first request_started
import post_request_task earlier so that it catches the first request_started

To be enabled for the current thread, post_request_task first needs to be
activated, as it defaults to being deactivated to make firing tasks from
non-request context such as management commands possible.

Activating it in a request-response cycle happens automatically thanks to
django's request_started and request_finished signals. Unfortunately, if
the request_started is triggered before post_request_task has been imported,
any tasks fired from that thread will be fired immediately, without benefiting
from post_request_task.

This is precisely what was happening before this patch, for the very first
request handled by each thread (so it was more commonly occurring when
deploying new code), because we typically import tasks deep in the code and
not at the top to avoid circular imports - so the import would take place,
just too late, after the signal had been fired.

mozilla/addons-server,wagnerand/addons-server,mozilla/addons-server,bqbn/addons-server,bqbn/addons-server,diox/olympia,wagnerand/addons-server,eviljeff/olympia,diox/olympia,eviljeff/olympia,diox/olympia,mozilla/addons-server,bqbn/addons-server,mozilla/olympia,wagnerand/addons-server,diox/olympia,eviljeff/olympia,mozilla/olympia,mozilla/olympia,wagnerand/addons-server,mozilla/olympia,eviljeff/olympia,mozilla/addons-server,bqbn/addons-server