Freeing up large storages while keeping provenance

[agoscinski]

We have the problem that people have large aiida storages and at the moment deleting files to reduce the size, destroys the provenance, this issue collects solutions to reduce storage size while keeping still keeping the provenance connection intact.

• Node contraction Node contraction for node deletion while keeping provenance #7569
• Purging repositories Delete repositories for freeing up storage space #7575