Add Radar Reflectivity Parameterization from WRF

### What is the feature/what would you like to discuss?

We would like to add a radar reflectivity calculation from WRF. This is a bit involved (2 different modules + an interface) and is best put in as a separate parameterization. It just needs state variables, and will output a diagnostic, so it can be called in physpkg after the microphyics. It might want a namelist switch so it can be shut off if not used.

I will attempt to do a first cut of this code in the current latest tag (cam6_3_082) and pass off to Kate and Bill Skamarock if necessary.

Feel free to ask questions.

### Is there anyone in particular you want to be part of this conversation?

@Katetc @skamroc

### Will this change (regression test) answers?

No

### Will you be implementing this enhancement yourself?

No