Allow filtering courses by Grading Basis

[kokrui]

This has historically been a very common request, and as of last year (#3427) we finally have a field from the API to definitively tell us whether a course is letter-graded or CS/CU.

Let's do it!

Relevant files:

• https://github.com/nusmodifications/nusmods/blob/master/website/src/views/modules/ModuleFinderSidebar.tsx
• https://github.com/nusmodifications/nusmods/blob/master/website/src/types/modules.ts

[chew01]

Had a cursory look and cmiiw the gradingBasisDescription will also need to be indexed in ElasticSearch else we are not able to aggregate by that field.

https://github.com/nusmodifications/nusmods/blob/master/scrapers/nus-v2/src/services/io/elastic.ts

[kokrui]

Yep! I'm thinking it may be easiest to just include the grading basis as an attribute of ModuleInformation

(as an aside, the different types defined in https://github.com/nusmodifications/nusmods/blob/master/scrapers/nus-v2/src/types/modules.ts should really be better-documented)

[chew01]

Re: documentation I think Swagger was meant to cover that at one point but it's clear that the schema there is outdated too 😅 If time permits (and the project is more active again) this is a good thing to work on 💯

[kokrui]

let's goooooooooooo @chew01 🚀🚀🚀