Toggle JSON logging

[kazauwa]

Feature request

Allow to opt-in for JSON logs so they can be easily parsed.
I think the implementation is pretty straightforward, and I can get it done over the weekend.

[kazauwa]

I suppose the implementation could be something like that:
https://github.com/juanfont/headscale/compare/main...kazauwa:feature/json-logs?expand=1

Setting json_logs to true swtiches to default zerolog formatting:

{"level":"info","path":"/var/lib/headscale/private.key","time":1655553834,"message":"No private key file at path, creating..."}

[iSchluff]

this seems useful, would you mind creating a pull request?

[kazauwa]

Done
Didn't want to create a PR before hearing from maintainers

[iSchluff]

not a maintainer, just keen on this feature :)

[juanfont]

Merged #768