NREL mismatch losses model due to non-uniform irradiance of cells

[echedey-ls]

Is your feature request related to a problem? Please describe.
Add a the model described here. Eq. 7 is the relevant one.

Describe the solution you'd like
A function with it's input "relative mean absolute error" in pvlib.pvsystem (other losses models live here). Documentation/example would add the extra mathematical layers since they can vary. In the upcoming PR I will show cases of this.

Describe alternatives you've considered
Including the RMAD calculation in pvlib.tools, but I think it doesn't make much sense to add such a mathematical function. In the example it can be supplied.
The proposed model could also have a place in pvlib.bifacial.

Additional context
I'm adding an example case with data from an HSAT mock-up my thesis tutors made.

[kandersolar]

See also #1541 (should we close this one as a duplicate?). The cited reference there (Prog in PV) is probably better than the EU PVSEC proceedings.

[echedey-ls]

Definitely. Thanks for the reference @kandersolar !