Fix logic used to determine project export status

Currently, lock files are used to determine the state of a
project export. However, the lock files are not stored in a shared
volume, causing the export states to be reported incorrectly.

In order to fix this, we now store the export states in database
as a more reliable mechanism. The table used is project_export_jobs.
It stores the project_id, job_id and the current state.

In addition to existing states, also added are two new states
queued and regeneration_in_progress states. They are used to indicate
a job that's waiting to be started and the case when a project export
operation has been requested to be re-generated.

Failed jobs are re-tried 3 times, after which the state is updated
to failed.

To account for jobs that get stuck, a cron job runs every hour
to set the stuck jobs to failed state.

Closes https://gitlab.com/gitlab-org/gitlab/issues/32203