Pseudo-Voigt: Compound Model or functional_models

[Ajb2307]

What is the problem this feature will solve?

The “Pseudo-Voigt” equation is a linear combination of the Gaussian profile and Lorentzian function. It offers a less complex alternative to the Voigt function and gives the user parameters of the mixing coefficient between Gaussian profile and Lorentzian function, equivalent width, and depth of the feature.

We found it the best option for evaluating alkali absorption lines in the near-infrared, but it is currently unavailable on Astropy (see poster linked below)

Describe the desired outcome

This could be added to AstroPy in Compound Model or functional_models as there is significant use of this model in the astronomical community and is a natural progression of AstroPy's modeling tools that already include the Voigt profile, Gaussian profile, and Lorentzian Function.

Additional context

https://aas243-aas.ipostersessions.com/Default.aspx?s=FA-8F-E2-DC-BE-FF-45-08-3E-48-E5-33-FC-E3-B1-E6

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[pllim]

Thanks for the idea! Sounds reasonable if someone wants to propose a PR to implement this (along with tests). I think this falls under a very old discussions in #981 to expand modeling to include other useful models.