consider moving definitions.json to web5-spec

[jiyoonie9]

          JSON schema supports remote references (`"$ref": "{url}"`) for definitions, so we would add the definition in web5-spec, deploy it and add the reference here. But it doesn't need to be a blocker on this PR, but at the least we should open an Issue to track it b/c I believe that's the ideal architectural solution.

Originally posted by @KendallWeihe in #364 (comment)