rgw/lc: add coroutine support for cloud-transition and cloud-restore

rgw/lc: add coroutine support for cloud-transition and cloud-restore

LCWorker's cloud-tiering was blocking the io_context on every HTTP
call, so rgw_lc_max_wp_worker coroutines ended up running one at a
time instead of in parallel. Same story on the restore side.

Pass the worker's optional_yield through RGWLCCloudTierCtx and use it
from the stream classes, the multipart and status-obj helpers, and
cloud_tier_restore. Transitions and restores now actually yield.

Signed-off-by: Matthew N. Heler <matthew.heler@hotmail.com>