Update the issuedTo internals

[pcothenet]

What

• Use a reference for issued_to in the swagger in order to avoid creating duplicate models

Why

• Cleaner internals

SDK Release Checklist

• Have you added an integration test for the changes?
• Have you built the library locally and made queries against it successfully?
• Did you update the changelog?
• Did you bump the package version?
• If endpoints were removed, did you manually remove the corresponding files? (this should be rare)
• For breaking changes, did you plan for the release of the new SDK versions and deploy the API to production?