get_SDA_property: generic aggregation of arbitrary `component` or `chorizon` child tables

[brownag]

This issue is a follow up from discussion in #399 to create a generic interface for child table aggregation at either the component or chorizon level

Example use cases that would be supported:

• Sum of Component Surface Fragment Cover %
• Sum of Component Horizon Fragment Volume %
• ...

Standard SQL aggregations like SUM/MIN/MAX/AVG would be able to be selected as needed. Possibly we could support some other custom functionality like a weighted average, but would need to add an argument to handle the weights column.