Enable use in analysis of the ICD code breakdown by parts that is present in database

[adamcantor22]

Is your feature request related to a problem? Please describe.
The SQL database stores ICD codes into 3 hierarchical parts. This makes sense, as ICD codes get more specific as more characters are included. However, as far as I can tell this is purely a database feature, and there is no way to incorporate this into analysis.

Describe the solution you'd like
When generating joined metadata files, split the ICD codes into the subgroups that exist in the data

Additional context
This is related to multiple existing issues. The problem of how ICD codes are inputted (which will affect expression in joined metadata) is in #214. This will also need to be modified based on the (maybe someday) upcoming large changes to metadata #432.