Element call disturbes normal phone call

**Is your feature request related to a problem? Please describe.**
When i have an active gsm phone call, i get disturbed by an element call when someone calls me.

**To Reproduce**
1. Start a normal phone call
2. Call the account in element app
3. Phone rings in earphone / internal speaker and disturbes your active phone call

**Expected behavior**
Get not disturbed by incomming element call.

**Describe the solution you'd like**
Silent notification or block element call. No overlay in current conversation.

**Describe alternatives you've considered**
Option to select action what happen when active phone call and incomming element call. Most times you have client installed on phone and desktop and can see notification afterwards.

**Smartphone (please complete the following information):**
- Device: all, my case Huawei Mate 10, also tested on Google Pixel 3
- OS: Android 10

**Additional context**
- Play Store 1.1.0 [40101002] (G-b1380)