Add support for simulating (e)BOSS

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](https://github.com/desihub/specsim/blob/228e503b44960412db81fea26955ddca2d5641b6/specsim/data/config/desi.yaml#L53). Most of the tabulated data is plotted here:


Start with the instrument section of data/config/desi.yaml and review the linked DESI instrument data as the reference. Define the required eBOSS inputs, create data/config/eboss.yaml, and determine whether a separate ebossmodel package and distinct BOSS, eBOSS, or SDSS configurations are needed. Done means eBOSS simulation support has the necessary configuration and input files.

Written by the indexing model from the issue text.