Add missing message type

[rcbgr]

Motivation

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Fix the OpenAPI spec

Change Summary

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Remove empty whitespaces and register the type on the message type. I generated a go client and before this fix, it would not compile.

Merge Checklist

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• [ ] PR title adheres to the conventional commits standard
• [ ] PR has a changeset
• [ ] PR has been tagged with a change label(s) (i.e. documentation, feature, bugfix, or chore)
• [ ] PR includes documentation if necessary.
• [ ] All commits have been signed

Additional Context

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PR-Codex overview

This PR updates descriptions and schemas in the spec.yaml file for UserData and OnChainEvents.

Detailed summary

• Updated descriptions for UserData and OnChainEvents
• Adjusted response schemas based on parameters
• Added clarity on optional parameters and response types

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