Add support for simulating (e)BOSS

[dkirkby]

As of v0.3, this is just a matter of creating eboss.yaml and collecting the necessary input files (which should go into a separate ebossmodel package).

Is there any need to have separate configs for BOSS and eBOSS? Would it be useful to also have an SDSS config?

For the list of config data needed to define the instrument, see the corresponding list for DESI in the instrument section of desi.yaml. Most of the tabulated data is plotted here: