Avoid common failure modes

[Mark-Simulacrum]

This changes two things that @jonas-schievink hit recently:

• Changes the default to replacing, rather than appending to existing collected data (on CI, we still append)
• Adds the default database path to the server, matching the collector.

[Mark-Simulacrum]

One detail pointed out on Zulip is that if we by default overwrite, the chances of deleting just-collected data are pretty high. It's not entirely clear what a good solution is yet, though.

[jyn514]

I would be happy with a way to opt-in to overwrite, instead of making it the default. Right now the only way to do that is to manually mess with the sqlite database.

[rylev]

Going to close since this is a bit stale. Feel free to reopen if you'd like to continue working on this (or if you think this should be rebased and re-reviewed).