Move file upload outside db transaction during project import

What does this MR do?

Large project imports fail due to file upload being inside a db transaction, which time outs when project archive is big, which results in project import failure.

This MR moves file upload outside of Project.transaction.

Related issues: https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/7904 https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/8383

Issue: #34091 (closed)

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• [-] Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content