Flatten namelist

[charleskawczynski]

Based on where it seems parameter calibration design is moving, and writing more general-purpose arg parsing for cli options, it seems like flattening the namelist would provide several benefits.

Can we discuss this a bit here?

cc @yairchn, @trontrytel, @ilopezgp, @odunbar, @costachris, @haakon-e

[trontrytel]

@charleskawczynski we will start with this one but be working on those issues in ClimaAtmos TC not here. I'll open an issue there. After talking to @dennisYatunin we will try to make it broader and try to improve our handling of TC arguments:

• introduce some hierarchy via arg parsing
• try to define the defaults only in one place