Default notification settings for incoming Element calls

### Steps to reproduce

1. Where are you starting? What can you see?
I've downloaded the F-Droid version of Element and installed on my as well as on my wife's phone to stay in contact. We're using a private instance with a private ntfy server. We're getting notifications for messages, however call notifications will only be received after the call attempt has already been revoked.
2. What do you click?
- Install Element
- Configure account
- Have some chats
- Try to make a voice or video call
- Call notifications are **only visible when device is unlocked and Element Android app is open / active**

### Outcome

#### What did you expect?
I expect Element to create a similar behavior for audio and video calls as when receiving a normal / Signal / Threema / WhatsApp / whatever call - there should be a constant ringing until the call is accepted, even if the device is locked.
#### What happened instead?
There's a simple notification after the call attempt is revoked.

### Your phone model

Google Pixel 7a

### Operating system version

GrapheneOS - Android 15

### Application version and app store

Element Version 1.6.30 [40106302] (F-73a0ec7f) F-Droid

### Homeserver

Synapse 1.124.0

### Will you send logs?

No

### Are you willing to provide a PR?

Yes