Added custom steps to const and support for float numbers

[ChristophPech]

Fixes:

• changing number.victron_settings_ess_maxdischargepower error: required argument is not an integer #48
• Battery min SOC - input #18
• number.victron_settings_systemsetup_maxchargevoltage is now 0.1 precision

[michaelkuty]

tested with my setup

[sfstar]

Thank you for opening this PR.
The changes seem to be OK.
However, I currently don't have the time to test them myself.
Since @michaelkuty tested it with his setup I will merge this change and create a release for it

[michaelkuty]

I'm using this branch and for me it seems to be working, at least we can set SoC and other values by sliders which were broken in your current main branch, but I cannot guarantee that it will not break something else

[michaelkuty]

and thank you for merge/release I think that could help to boot up community to help us make it better/stable