rgw: copy object data if target bucket is in a different pool

Fixes: #9039
Backport: firefly

The new manifest does not provide a way to put the head and the tail in
separate pools. In any case, if an object is copied between buckets in
different pools, we may really just want the object to be copied, rather
than reference counted.

Signed-off-by: Yehuda Sadeh <yehuda@redhat.com>
rgw: copy_obj_data() uses atomic processor

Fixes: #9089

copy_obj_data was not using the current object write infrastructure,
which means that the end objects weren't striped.

Signed-off-by: Yehuda Sadeh <yehuda@redhat.com>
rgw: pass set_mtime to copy_obj_data()

Sometimes we need to set the mtime when copying object data (e.g., when
we rewrite the obj).

Signed-off-by: Yehuda Sadeh <yehuda@redhat.com>
rgw_admin: add --min-rewrite-stripe-size for object rewrite

A new param to check whether the object has requires restriping,
checking whether a specific object stripe is bigger than the specified
size. By default it is set to 0, and in that case it'll always be
restriped. Having it set to 4M + 1 will make sure that only the objects
that weren't striped before (using default settings) will be restriped.

Signed-off-by: Yehuda Sadeh <yehuda@redhat.com>