Add the possibillity to put the call on hold

Add the possibillity to put the call on hold when tranferring a call using the Webex desktop app.

When transferring a call using the Webex app, currently the call is not being put on hold and the caller is able to hear the audio from the called party, which is not the case when using Cisco desk phones. It would be beneficial to add the option for the call to be put on hold when transferring or make it like this by default.