Allow multiple voicemail greetings on individual user lines Merged

In the messages section per user, we should be able to add more greetings so that I can add a vacation message to switch to when I'm away. Going through the custom rule and changing other settings is much too involved. Every other phone system I've used has allowed for this so I don't have to rerecord my greeting when I want to just change it for a week, or go through multiple steps to do so.