Log improvements

It would be very beneficial to automate sending of logs. Some gradual improvements we can do are:

• Add log rotation (right now there's a single log that can grow a lot, with potential sensitive leaks when users upload it to a public issue).
• Diagnostics utility: quality of issues can be greatly increased by automatically fetching a) Release string, b) os/desktop, c) installation method, d) polkit processes running etc...
• Log scrubbing (for potentially sensitive data).
• Log viewer: open a Qt window with the latest log.
• Log sending: this is perhaps the more complicated part. We can try to integrate with gitlab reporting mechanisms, or upload to some custom service (it'd be ideal, I think, if whatever solution returns a code that uniquely identifies a given log and it can just be referenced from an existing issue).

We can leave this "meta" issue as a reference for the epic, and create individual issues to keep track of each feature.