Add Project Uploads Migration to BulkImports

What does this MR do and why?

⚠ depends on !71586 (merged)

⚠ this feature is behind bulk_import_projects feature flag which is off by default (and on .com).

Mentions #339401 (closed)

This MR adds Project Uploads to Project Migration feature (that is part of Group Migration feature https://docs.gitlab.com/ee/user/group/import/ which ~"group::import" is working on) and imports all project's uploads (except avatar). The GitLab Migration tool allows you to migrate your groups (subgroups and projects) with one click. This MR adds handling of project uploads.

Screenshots or screen recordings

projectuploadsmigration2

These are strongly recommended to assist reviewers and reduce the time to merge your change.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

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