Add setting to disable file logging

[ahmershahdev]

Adds an “Enable logging to file” setting, enabled by default, so users can disable vorta.log and keep logging only to the console/journald.

Includes tests for toggling the setting and file handler behavior.

Tested on my fork before opening this: lint, mypy and the full test suite pass on Ubuntu and macOS (CI run). One of the new tests checks that no vorta.log is created while the setting is off.

Fixes #1705

[m3nu]

Thanks, this follows the approach discussed in the issue. Two things before merging:

1. Background mode: init_logger(background=True) adds no console handler. With --daemonise/autostart and file logging off, Vorta logs nowhere, but the tooltip says logs go to the console. Please keep a console handler in background mode when file logging is disabled, or at least adjust the tooltip.
2. Startup order: init_logger() runs before init_db(), so the setting is only applied at the end of init_db(). Anything logged before that, such as recovering interrupted jobs or migrations, still goes to vorta.log. Applying the setting right after init_db() in __main__.py, or reading it there before attaching the file handler, would close that gap.

[ahmershahdev]

Thanks for your feedback, I've fixed both points: in background mode, logs now go to the console when file logging is off, and the setting is now read before the file handler is attached, so nothing from init_db() ends up in vorta.log.