Body request property previewText not present in CreateEmailCampaign nor UpdateEmailCampaign

[Innsai]

          In the API Reference (https://api.brevo.com/v3/emailCampaigns) when creating the Email Campaign you can send in the body of the request a property called previewText (Preview text or preheader of the email campaign). There is no such property in the definition of CreateEmailCampaign.

Originally posted by @Innsai in #66 (comment)