Add "sections" aggregate endpoint to course endpoint

[jpahm]

Currently, it can be inconvenient and overcomplicated for our end users to perform some common aggregate operations such as getting all of a course's sections.

As such, we should add the following endpoints which immediately aggregate and return matching courses' sections:

• Query based: GET /course/sections (allows for querying like the base course endpoint)
• ID specific: GET /course/{courseId}/sections (gets sections only for a specific course)

[mikehquan19]

Can I be assigned this ? This is fun.

[jpahm]

Can I be assigned this ? This is fun.

I'm glad it's fun, the work on these issues is very helpful!

You are good to work on it :)

[mikehquan19]

I completed this task and committed it in the same pull request as task #230.
Thank you.