Add aerosol optical depth to AerosolState

[charleskawczynski]

This PR adds aerosol optical depth to AerosolState.

@szy21, can you please let me know if this looks like I'm on the right track, or if there are changes needed here?

[szy21]

Yes, this looks like the right direction. We only need the vertical sum of AOD though, not every layer. And I think if you could output AOD in this test: https://github.com/CliMA/RRTMGP.jl/blob/main/test/all_sky_with_aerosols_utils.jl, it would be a good step towards having it in ClimaAtmos.

[charleskawczynski]

@sriharshakandala, can you please take a look at this?

[sriharshakandala]

pseudocode

    band_wv_550nm = 1 / band_550nm
    bandidx = 0
    for i in 1:nband
        if bnd_lims_wn[1, i] <= band_wd_550nm <= bnd_lims_wn[2, i]
            bandidx = i
            break
         end
    end