[FEATURE] More auto_shutdown_level options (<50%, <70%)

[oboote]

Is your feature request related to a problem? Please describe.
Current list of auto_shutdown_levels is too restrictive (max <30%).

Describe the solution you'd like
I would like to trigger a safe shutdown when much more battery is available (for example, <50% or even <70%).

Describe alternatives you've considered
I tried setting via nc using set_safe_shutdown_level 50 but values higher than 30 are ignored.
I tried setting in /etc/pisugar-server/config.json but this gets overwritten by webUI and probably doesn't actually get sent to the pisugar (tbd).

Additional context
That's all :)