Reinstitute common embed definitions

[bjester]

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Current behavior

We rolled back separating some common schema definitions (solely a UUID definition) into a separate file because it was not supporting both frontend and backend usage.

Desired behavior

Separate out some common embed definitions, including more than just the previous UUID definition, and structure it similarly to how completion criteria uses mastery criteria, such that we can utilize the schemas on both the frontend and backend.

• Since le-utils does not have a hard requirement on jsonschema itself, any usage should be overly defensive on it not being installed

Value add

• DRY

Possible tradeoffs

• Complexity of separating schema definitions into more than 2 files