GraphQL should have the ability to query for a course/section's info based on courseHash/sectionHash

[NEUDitao]

This is so that for the notifying service, we're able to validate a course exists when we get data.

[NEUDitao]

Spec should be similar to what's laid out #5 . As in:

If I send a query of

{
   courseHash: string;
}

I should receive a response of

{
  courseCode: string;
  courseHash: string;
  term: string;
  numberOfSectionsAdded: number;
  campus: string;
};

and if I send

{
   sectionHash: string;
}

I should receive

type SectionNotificationInfo = {
  courseCode: string;
  sectionHash: string;
  term: string;
  seatsRemaining: number;
  crn: string;
  campus: string;
};

[gamburgm]

thanks @megandouli!