Support light terminal colour schemes

[jotaen]

As pointed out in https://github.com/jotaen/klog/discussions/288, klog’s default output colouring is geared to dark terminal backgrounds.

As far as I know, there is no portable/reliable way to detect the background colour of users’ terminals at runtime.

One rather simple approach could be to add an option to the configuration file (see klog config / klog config --help), along the lines of:

colour_scheme = light

The default would be dark (as it effectively is now), but users then could overwrite it.