"
Cache cf mappings when breaking in the middle of a segment sending so
that the sender has them the next time it wants to send this segment
for where it left off before.
Also add the "discard" metric so that we can track hints that are being
discarded in the send flow.
"
Fixes#4122
* 'hinted_handoff_cache_cf_mappings-v1' of https://github.com/vladzcloudius/scylla:
hinted handoff: cache column family mappings for segments that were not sent out in full
hinted handoff: add a "discarded" metric
(cherry picked from commit 88c7c1e851)
cf4b4d4878