rgw: configurable chunk size

Fixes: #7589

Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
ReplicatedPG: disable clone subsets for cache pools

To do this properly, we need to take appropriate read
locks on clone sources and handle evicted clones.

Fixes: #7874
Signed-off-by: Samuel Just <sam.just@inktank.com>
Merge remote-tracking branch 'origin/wip-7874' into wip-sam-testing