feat: detect muted devices

[d0minYk]

Plugin version:
2.1.0

Platform(s):
iOS

Current behavior:
iPhones that are silenced with the physical mute button won't play any voice, no warning shown either

Expected behavior:
iPhones would override the silence option, or there would be an isMuted function that returns whether the phone is muted/not on iOS, so a warning can be shown.

Steps to reproduce:

1. Put an iPhone in muted mode with the physical button
2. Call the speak function with anything