Add Management Command to change file ref for in-place imported files to s3

Problem

We run a Funkwhale instance for years and now decided to move the storage to S3. Now, its kind of easy to achieve this for files that have been uploaded, since their reference is relative to the storage backend configured. We therefore just need to move the files to S3 and configure it accordingly. However, everything that has been a in-place import isn't that easy, since the file is references directly. Currently there is no built-in way to move those files and update the references

Solution

We need a management command that can be run after the files have been copied to S3 which makes sure the references are updated accordingly.