When push/pull media references, have an option to not push/pull the actual files, move just the references.

[ctolkien]

This is somewhat related to #236 and may be tied together.

Describe the solution you'd like
For a site we are evaluating uSync.Complete for, it has ~50gb of media on Azure blob storage. When we are moving media between environments, we would like the option for uSync to only port the reference to the media, not the media itself. We have other means of moving the media which does not involve downloading it. Using azcopy for moving content between storage accounts or blob replication, etc.

This would ideally then vastly speed up the time that it takes to push/pull media, as it does not need to take into account moving any of the bits around for the media itself.

Describe alternatives you've considered
We've tried to pull large amounts of media between different servers, it uses a lot of bandwidth, uses a lot of egress ($), and in several occasions caused the server to out of memory exception. We also have a 4 minute request limit imposed by Azure Container Apps, which does not leave enough time to move the media. We've had to run the process 15x, moving slightly more each time.