rgw/s3website: Fix ErrocDoc memory leak.

rgw/s3website: Fix ErrocDoc memory leak.

Yehuda pointed [1] out a memory leak with the RGWGetObj not being handed back, and
suggested that shared_ptr was used to handle it, rather than the prior approach
of explicitly calling handler->put_op.

This commit implements just that change, in isolation from other changes, for
ease of comparision testing.

X-Reference-1: https://github.com/ceph/ceph/pull/8669#discussion_r63445516
Signed-off-by: Robin H. Johnson <robin.johnson@dreamhost.com>