Support single griddap dataset with 2d and 1d variables.

[ChrisJohnNOAA]

This needs some investigation on if and how to implement the feature. Original message below:

Pinging @ChrisJohnNOAA is this capacity that @jklymak describes something ERDDAP can support/could support in future?

As I understand, the desired behavior is to have a single griddap dataset which serves 2-D gridded variables like temperature(profile_num, depth_bin) as well as 1-D variables like lat(profile_num), without broadcasting these 1-D variables to 2-D.

At the moment, from reading the docs @rmendels highlighted ( In EDDGrid datasets, all data variables MUST use (share) all of the axis variables.), it seems this is not currently supported. So you would have to create two different datasets on your ERDDAP server to achieve this.

Originally posted by @callumrollo in https://github.com/ERDDAP/erddap/discussions/177#discussioncomment-10180612