Logging

Rustysd needs persistent logging. This needs some questions answered:

1. Should rustysds logs go somewhere else than stdout/stderr output of services?
2. Should each service have it's own log or should it all be in one file?
3. Can/Should rustysd just reuse systemd-logind?

Update: I meant systemd-journald of course!

No files or tests are named. Start by resolving whether logs should remain on service stdout/stderr, be split per service or combined, and whether systemd-journald should be reused; done means the logging design and persistent behavior are clearly defined and implemented.

Written by the indexing model from the issue text.