If we dump journalctl logs, we should dump them in .journal binary format, not json #9

Dumping all journalctl in raw .json format makes things more difficult to eyeball and reason about chronologically for me - it's better for jq parsing if you already know what you're looking for, but harder for thinking/eyeballing/studying the holistic log - I prefer flat log format for this.

Suggest we split the difference and capture journalctl logs in the original .journal binary format, and save those in the bundle - from those, anyone with the bundle is free to export those .journal files to the textual representation that's most useful for them locally - json, flat, or anything else the journalctl binary supports.

This also makes it easier to export time-based subsets of the log as well.