This method copies existing emails of the project into one of its email folders. The originals do not change.
A copy keeps the content, the subject, the preheader and the language of its original; its language versions are
copied along with it. A copy keeps the name of its original, as a copy made in Stripo does, also in the folder of the
original, and has no author, the same as emails created through the API. To rename copies, use Update name,
subject and preheader of emails.

• Up to 100 ids in one request. All copies go to the same folder; without folderId they go to the root of the project.
• The plan limit is checked for all copies at once: if the plan has no room for every copy, none is made.
• A copy takes the content saved at the moment of the request: unsaved changes of an email opened in the editor
  are not copied.

The copy runs in the background: the response carries an operationId, and the outcome is read with Get the status
of an operation within 15 minutes. result.copies tells which copy was made of which original; result.failed
lists the ids that were not copied: not found in the project (NOT_FOUND, also for an email of another project
or one deleted while the copy waited for its turn), a draft (DRAFT), a translated version (TRANSLATION_VERSION)
or passed more than once (DUPLICATE_ID). The
copy is all or nothing: if it fails, no copy is kept and the status is FAILED.