osd/ReplicatedPG: release op locks on on commit+applied

We were releasing the op locks when we applied the update but (potentially)
before we committed it.  This means that another client can read object
state that is not yet durable.

Fixes: #7709
Signed-off-by: Sage Weil <sage@inktank.com>
Merge pull request #1454 from ceph/wip-7709

osd/ReplicatedPG: release op locks on on commit+applied

Reviewed-by: Samuel Just <sam.just@inktank.com>
Reviewed-by: Greg Farnum <greg@inktank.com>