roll over logs / fix filling up /tmp with logs

[raphCode]

• rolls over at 20 MB into zellij.log.old.0
• fix Logging may fill up /tmp mount until all zellij instances are closed #1410
• unsure what happens with multiple zellij instances, probably they all copy over the same old log?
• do we need to update the issue template to tell users to include the old log?

[imsnif]

Cool! Honestly, I cannot imagine a scenario in which we need (or even will need) more than 100KB of logs. I think we can cap it there and delete the rest.

[raphCode]

changed the cap, now we have max. 100 kB in a file.
In case the log just rolled over, we still have the old 100 kB log so the user can always post enough logs in an issue.