Improve naming in the blob spec

[Gozala]

Per storacha/w3up#1342 (comment)

Reading this PR got me wondering if perhaps we should have used memory/allocate and memory/commit instead (which would avoid confusion between service blob and user blob) that way address: BlobAddress would have changed to memory: AllocatedMemory

I think it is worth doing, especially because while discussing federated storage network it came clear that w3up will likely look for a suitable storage node candidate(s) and perform allocation with them. That is to say memory/allocate and memory/commit would make even more sense then. On the other hand space parameter makes very little sense in that context.