Add more data validation tests

[aomi]

Determine which fields are required and optional. ie. we expect the CRN to be present for every Section etc. etc. Currently we only do simple validation of fields but we should extend this to every attribute and categorize them as required or optional.

This will help us reduce the chance that we provide inaccurate data.

An example of this being done can be seen src/pages/courseListingEntries/__tests__/index.test.ts.
A good first step would be make a general data validation function for each type.
Secondly, analyzing each property (like crn) across all sections, classes etc. and analyze the values they are assigned.

For example, we currently don't know what the instructors is formatted like and if we can do any further data extraction. So far, this instructors attribute usually has a (P) likely showing that they are a professor but it would be nice to see if there are any others like this.