Changes to Get issue relations

added the optional property code to the response with the 400 status

added the optional property code to the response with the 401 status

added the optional property code to the response with the 403 status

added the optional property code to the response with the 404 status

added the optional property code to the response with the 500 status

added the required property items/items/related/namespace/allOf[subschema #1: PartialNamespace]/slug to the response with the 200 status

added the required property items/items/related/created_at to the response with the 200 status

added the required property items/items/related/updated_at to the response with the 200 status

endpoint added