Restrict number of allowed project exports in a period
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[According to Kibana](https://log.gprd.gitlab.net/app/dashboards#/view/03a11c50-ba46-11ec-b73f-692cc1ae8214), some projects are exported several times in a short period. Since exporting projects consume a lot of resources, we should consider limiting the number of times a project can be exported.
For example, there are cases of projects being exported 40 times in a period of 7 days, on average, five exports per day or one every 4 hours.
Apparently, users are using Project Export as a disaster recovery tool, and I believe one reason is our [documentation](https://docs.gitlab.com/ee/user/gitlab_com/#backups) recommends using Project Export as a backup solution. However, I don't think the tool was built with such intention at least the [MR](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/41788) that introduced such information doesn't explain why we decided to suggest Project Export as a backup solution.
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