Check for full before changing the cached obc

Check for full before changing the cached obc

ReplicatedPG::prepare_transaction(): check if the pool is full before
updating the cached ObjectContext to avoid the discrepancy between
the cached and the actual object size (and other metadata).
While at it improve the check itself: consider cluster full flag,
not just the pool full flag, also consider object count changes too,
not just bytes.

Based on commit a1eb380c3d5254f9f1fe34b4629e51d77fe010c1

Fixes: #13335
Signed-off-by: Alexey Sheplyakov <asheplyakov@mirantis.com>