Add rake command to migrate archived traces from local storage to object storage

What does this MR do?

This MR adds gitlab:traces:migrate rake task to migrate archived traces from local storage to object storage. If users didn't use the object storage integration from the beginning, job traces were archived but stored in local storage. Currently, there are no ways to migrate such archived-but-locally-persisted traces.

What are the relevant issue numbers?

Close https://gitlab.com/gitlab-org/gitlab-ce/issues/50232

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides