crimson/osd: move get_max_object_size() to store level

crimson/osd: move get_max_object_size() to store level

is_offset_and_length_valid() called get_sharded_store() locally to
obtain the store-specific max_object_size. On alien cores (where
smp::count > store_shard_nums), the local store is inactive and the
call hits assert(shard_store.get_status() == true).

As the max object size is a store-specific property and not a
store-shard one, there is no reason to acquire the
store shard to obtain it. Instead -
a get_max_object_size() method is added to the Store interface.

Fixes: https://tracker.ceph.com/issues/76946
Signed-off-by: Ronen Friedman <rfriedma@redhat.com>