Migrate legacy uploads rake tasks

What is included in this MR

Original MR: !24679 (merged)

There are some uploads that were uploaded using AttachmentUploader which is not supported anymore.

This MR adds rake task to migrate them to the "new" location, under a proper project directory.

Migration failed due to validation problems on dev #62982 (closed)

If the database contains notes with invalid noteable values, the background migration would fail repeatedly, causing duplicate "failed to migrate" text to appear in LegacyDiffNotes

Fixed by: !29389 (closed)

Update

New rake task migrates uploads created for legacy_diff_note records as well.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and testing

• [-] Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team