KAZOO-3217: conferences: play name on join feature

If the metadata fails to save, what happens to the caller? If this process crashes, the caller will be stuck with dead air, not join a conference, and it will be weird and awkward. Perhaps the code should account for a failed write? Maybe see what the error was and either re-record (or re-save) the name, or just place the caller into the conference with a generic "new caller has entered the conference.