Option to disable voice messages

#### Is your suggestion related to a problem? Please describe.
I don't use voice messages so I consider the possibility of accidentally sending an audio recording of my environment to a room where it's impossible for me to delete it a security risk.

#### Describe the solution you'd like.
A setting somewhere that completely disables voice messages for me. Preferably (but possibly optionally?) saved to my account data and respected by all my sessions in all Element clients across all platforms.

#### Describe alternatives you've considered.
- Deny microphone access to the Element clients and apps. Though this is not an ideal solution as I would have to explicitly enable mic access before and disable again after a call.
- Disable the feature on the Synapse or reverse proxy level. Tho I can't immediately think of a way to do this. But if this is possible, it is also not a good solution in case I do need voice messages some day and this is not available to people that are not running their own server.

No implementation files, tests, or entry points are named. Start by determining how Element clients share account settings across sessions and platforms, then define a complete disable-voice-messages setting whose effect is consistent across supported clients and can be reversed when needed.

Written by the indexing model from the issue text.