rgw: reshard: skip stale bucket id entries from reshard queue

rgw: reshard: skip stale bucket id entries from reshard queue

If we encounter a reshard queue entry that has an older ID compared to the
bucket's current ID, it'd mean that some other process or a manual reshard has
already processed this entry, skip processing the entry this time. An
alternative is to verify the num_shards that we have in queue >= the current
shards, but this would mean that we may reshard a recently manual resharded
bucket again which might not be intended

Fixes: https://tracker.ceph.com/issues/45134
Signed-off-by: Abhishek Lekshmanan <abhishek@suse.com>