docs: Provide meaning of course codes

[limlindsayj]

Description

Added openapi descriptions to excludeRestrictionCode and restriction.

Related Issue

#418

Motivation and Context

Currently there is no description or context for these in the schema. It is helpful to have a list of what these restriction codes mean in the description, or you would have to look it up yourself in websoc.

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code involves a change to the database schema.
• My code requires a change to the documentation.

[laggycomputer]

• Not sure why Wrangler is being addled with again (I'm sure something strange happened). Please revert.
• We're pasting in a somewhat critical string in two different places. Try not to repeat it: use a constant string, shared Zod schema, OpenAPI type reference, or something else.
• I don't exactly want to be responsible for the ground truth. What are your thoughts on just linking the WebSoc pages which lists these meanings?