Request SIZE as required attribute. Fixes issue with pinning
nearline files from PinManager CLI (or executuin p2p admin command)

Ticket: #8275
Acked-by: Paul Millar <paul.millar@desy.de>
Target: 2.2
Require-book: no
Require-notes: yes
Merge pull request #635 from DmitryLitvintsev/fix/2.2/pinstage

Fix/2.2/pinstage