LDV: add charging_efficiency condition

[dmuldrew]

:rocket:

• [ x] Is your feature request essential for your project?

Describe the workflow you want to enable

We would like have charging efficiency vary according to the power parameter input

Describe your proposed implementation, if applicable

1. Add the following condition:

   if power > 19.2, charging efficiency=0.95
   else charging_efficiency = 0.9

2. Make charging_efficiency a parameter in relevant functions instead using the value from const.py
3. Remove charging efficiency and ER values from const.py

Example in existing code can be found here: https://github.com/isond/PreREISE/blob/fc6ed851fc9fbdc0a65b309ab37aa51bbfe8a84c/prereise/gather/demanddata/transportation_electrification/smart_charging_HDV.py#L261

Additional context

Add any other context or screenshots in this section, e.g., a plot from an article you believe would clearly communicate results.