Get a list of values for a metadata field

[machristie]

Implement an API method(s) to get a list of values for a metadata field. For a field with discrete values, this API method might just return all known values. However, for a field with continuous values, the API method should return a set of ranges of values (bins) where the number of records that fall within each range are roughly equivalent (similar to Pandas qcut function). The API method should provide a parameter for how many bins to return for continuous values.

We might want to add a "continuous or discrete" attribute to metadata fields API since this seems like an important thing to describe about a metadata field.

Also, when it comes to continuous data, that only applies to continuous data types like numeric and date-time data types.