feat: separation - endpoints for finalize & assign

finalize at:
    POST /v1.0/vaults/{vaultid}/files/{fileid}
assign at:
    POST /v1.0/vaults/{vaultid}/files/{fileid}/blocks
Since it's a bad vault, then it's the validation that is rejecting the request and therefore a 400 is returned per the PUT/POST Validation rules. Or should we change them all?

Presently GET Validation Rules will return 404 while PUT/POST Validation Rules return 400. This behaviour is consistent within Deuce right now.