Add AQI Support

[generallynonsensical]

Is your feature request related to a problem? Please describe.
With the prevalence of wildfires and other air quality contaminants, having the AQI/AQHI listed in the widget would be a great feature for all users. Especially those who are sensitive to AQI/AQHI changes.

Describe the solution you'd like
Add the AQI/AQHI to widget.

Describe alternatives you've considered
Other widgets but none are even close to this one.

Additional context
I am not sure if there are global standards, or if each country has their own measurements. From what I've seen, it's PM2.5 and PM10 that are used.

[k-donn]

Thank you so much for using the widget! I will be sure to add this into the KDE 6 version.