Add JSON Schema for learning objectives

[AlexVelezLl]

Summary

Adds JSON Schema for unit learning objectives and unit tests.

References

Closes #189.

Reviewer guidance

• Are tests running?
• Are tests testing the right things?
• Is the new schema following the issue requirements?

[LianaHarris360]

Thanks for your work on this @AlexVelezLl. Overall, the changes make sense to me and I appreciate the good test coverage. My only suggestions are for stricter regex for some of the field/string validations.

[AlexVelezLl]

Thanks @LianaHarris360! I have made the JSON schema spec more restrictive! Just one little question: What will be the identifier for the assessment questions that will be stored in this object? I have implemented the regex following the question item validator in Kolibri, since it seems the question_id is only unique within a quiz.

[LianaHarris360]

I doubled checked with Richard and he confirmed that the identifier for the assessment questions will either reference the assessment ids that are on the Studio AssessmentItem model) and be UUID4 or forced to be UUID5 in Ricecooker.

[AlexVelezLl]

Thanks @LianaHarris360! Just updated the PR! 👐