Update embed schemas for newly required fields

[bjester]

Summary

• Adds mandatory channel_id to the schemas, particularly important for the content embedding requests
• Ensured all IDs are now enforced as UUIDs (with dashes), which will require updates in Studio and CA API to add / remove dashes
• Enforces language is passed in topic embedding requests, and removes duplicitous ancestor definition to prioritize the one definition on the target topic

References

closes #158

Reviewer guidance

Test updates make sense?

[akolson]

Changes look correct to me. Thanks @bjester