Derive transactional.json from transactional.openapi.json

[jmoriarty-mc]

Summary

• Updates spec/transactional.openapi.json to v1.4.0
• Reformats spec/transactional.json to consistent 2-space multiline JSON style (cosmetic only, no semantic changes)

More commits to follow syncing request schemas, response schemas, and descriptions from the OAS3 source.

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