rgwlc: include lc shard oid in "lc shard list"

rgwlc:  include lc shard oid in "lc shard list"

E.g.,
[
    {
        "bucket": ":bucket1:f2f4a8dd-7ec9-4758-bc4f-c8f5fbc85109.4137.2",
        "shard": "lc.6",
        "started": "Fri, 18 Feb 2022 17:30:16 GMT",
        "status": "COMPLETE"
    },
...
]

The prototyped approach adds a copy of the shard name (which is
assured to be a small string) to rgw::sal::LCEntry.  It's not
expected to be represented in underlying store types.

Signed-off-by: Matt Benjamin <mbenjamin@redhat.com>