Allow project export to be imported using URL
<!--IssueSummary start-->
<details>
<summary>
Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards.
</summary>
- [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=21989)
</details>
<!--IssueSummary end-->
The new [project import API](https://docs.gitlab.com/ee/api/project_import_export.html#import-a-file) allows a project export to be imported using the API. It currently only supports multipart form uploads, which is not idea for large projects that could be multiple gigabytes large. We should add support for allowing a URL to be provided, like a presigned S3 URL.
### Proposal
Add support for providing a HTTP/HTTPS url to the project export to be imported
### Links / references
https://gitlab.com/gitlab-org/gitlab-ce/issues/41899
issue