Obsolete property in send email sample

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### This issue is for a: (mark with an `x`)
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- [ ] bug report -> please search issues before submitting
- [ ] feature request
- [x] documentation issue or request
- [ ] regression (a behavior that used to work and stopped in a new release)
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`poller.getOperationState().isStarted` was removed in a version of azure/communication-email as of the official Microsoft documentation points in favor of `poller.getOperationState().status !== "running"`. Reporting this here as the provided sample code still references this older property and may cause issues for developers who do not catch the notice in the documentation and rely solely on this sample.

Reference in MS docs: https://learn.microsoft.com/en-us/azure/communication-services/quickstarts/email/send-email?tabs=windows%2Cconnection-string%2Csend-email-and-get-status-async%2Casync-client&pivots=programming-language-javascript

Issue in sample code file: `send-email/send-email.js` Line 27

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Apri send-email/send-email.js alla riga 27 e confronta l’esempio con la documentazione Microsoft collegata. Aggiorna l’esempio in modo che utilizzi la proprietà di stato corrente del poller delle email, quindi verifica che il riferimento obsoleto a isStarted sia stato rimosso e che l’esempio rifletta ancora il flusso documentato.

Scritto dal modello di indicizzazione a partire dal testo della issue.