storage: escape hatch to ignore timestamps in future during retention #9820
Description
This is separate to a more structured change to record server timestamps in segments so that retention can be done reliably by server time rather than client time. That requires a format change, this ticket is for a backportable hack.
If a user has written timestamps into Redpanda that are far in the future, these can prevent collection of old data on retention.ms topics indefinitely.
To provide a way out of this situation, we may add an off-by-default configuration property that changes the retention behavior to ignore timestamps in the future (relative to the server's local time), and instead look elsewhere for a usable timestamp:
- If any other timestamp in a segment's index is not in the future, then use this.
- If all the timestamps available are in the future, then fall back to using the mtime of the segment file