Implement CMB Dipole component

[zonca]

It would be useful to have an implementation of the CMB Dipole as a separate component in PySM.

I have a simple implementation here:

https://github.com/CMB-S4/s4mapbasedsims/blob/master/202102_design_tool_input/utils/create_cmb_solar_dipole.ipynb

However it would be nice to also have the option of activating the frequency dependent quadrupole, see implementation in toast:

https://github.com/hpc4cmb/toast/blob/ddae67de4154067d2317999f6cf6c31dd48ae047/src/toast/todmap/todmap_math.py#L552-L556

So we could have:

• dip1: dipole without frequency dependence using NPIPE parameters 3366.6 ± 2.7 263.986 ± 0.035 48.247 ± 0.023 https://arxiv.org/pdf/2007.04997.pdf
• dip2: same as dip1 with frequency dependent quadrupole correction

@keskitalo @giuspugl @brandonshensley @seclark any feedback?

No hurry, it will be some time before I can start working on this.