hardcoded sensor_power_load_no_var_loads sensor name in utils.py

[scruysberghs]

Describe the bug
A clear and concise description of what the bug is.
Whet you set a custom sensor for sensor_power_load_no_var_loads in the the EMHASS config file:
you still get the error :

ERROR - emhass.web_server - The retrieved JSON is empty, A sensor:sensor.power_load_no_var_loads may have 0 days of history, passed sensor may not be correct, or days to retrieve is set too heigh

To Reproduce
Steps to reproduce the behavior
Set a non default sensorname in the configfile and run a mpc or day ahead optimizer without passing the non default sensorname as runtime parameter

Expected behavior
A clear and concise description of what you expected to happen.

Screenshots
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Home Assistant installation type

• Home Assistant OS
• Home Assistant Supervised
• Home Assistant Core

Your hardware

• OS: HA OS, Windows, Linux, etc
• Architecture: amd64, armhf, armv7, aarch64

EMHASS installation type

• Add-on, Docker Standalone, Legacy Python virtual environment

Additional context
Add any other context about the problem here.

Created a PR for what where I think the problem is, line 615 in utils.py reads
if "var_model" not in runtimeparams.keys(): var_model = "sensor.power_load_no_var_loads"
while it should get the sensorname from the config file

[davidusb-geek]

It makes much more sense to go fetch the sensor name on the configuration.
I don't know why this was hard coded like that.
Thanks for the PR