Design a policy on how takedown notices are propagated to mirrors

Now that Software Heritage has mirrors, it should design a policy on how removal from takedown requests (or serious software malfunction) are propagated to mirrors.

We might want to consider different possibilities depending on the kind of takedown requests. For example, child abuse images could be removed without supervision while copyright issues could need a manual review.

We could also make mirrors hide any data removed from the main archive until the requests are manually reviewed (and data then deleted or kept).

The case of cold storage mirrors should also be addressed.