Add the record timestamp. The timestamp is extracted from the row marker
of the mutation when we write it.
When inserting a record to index, we compare it with the existing
record, and insert it only if it has newer timestamp.
Add a segment sequence number that is a global (per-shard) increasing
number that is allocated when getting a new segment for write, and is
written in buffer headers in the segment.
It is used to distinguish between buffers written to different generations
of a segment, and for recovery to break ties by keeping the record
from the newest segment.
Refs https://scylladb.atlassian.net/browse/SCYLLADB-770
no backport - logstor is a new feature
Closesscylladb/scylladb#29933
* github.com:scylladb/scylladb:
test: logstor: add basic delete test
logstor: rewrite segment seq num from streaming
logstor: add segment sequence number
logstor: get_segment helper
logstor: compare records by timestamp
f8ac8540bd