os/bluestore: make shared blob fsck much less RAM-greedy.

os/bluestore: make shared blob fsck much less RAM-greedy.

Fixes: https://tracker.ceph.com/issues/44924
Signed-off-by: Igor Fedotov <igor.fedotov@croit.io>
(cherry picked from commit 8fddc8464ee4dbb0ee22a10de21e8c16f38bf1ed)
(cherry picked from commit a902d22b6c785099c704a229db1dc1e6fefee3e2)

 Conflicts:
	src/common/options/global.yaml.in
	src/os/bluestore/BlueStore.cc
        src/os/bluestore/BlueStore.h
	src/os/bluestore/bluestore_types.h
	src/test/objectstore/store_test.cc
caused by lack of ZNS stuff and using options.cc for config parameter
defitions rather than yaml file(s)