Add ability to catalog grid variables

[mgrover1]

In most of our parsers, we check to see if variables are time variant, excluding variables that aren't. Many of those variables relate to the grid, which would be useful to include in the data catalogs. See this code snippet below which excludes the time-invariant variables

if time in da.dims and v not in {time, time_bounds}

We could specify these variables to be "static" or some better name... the case this would especially help with this is MOM data which stores the grid variables in separate static file, which often times has its own stream.