Add changelog for 12.0.0-rc.1

[nickvergessen]

✅ Added

• Add support for simulcast streams when the high-performance backend is used #5535
• Allow users to have multiple session in the same conversation #5194
• Voice messages, location sharing and contacts sharing #5610 #5573 #5731
• Play a sound when a participant joins or leaves the call #5410
• Add unread message marker in the chat view #3825
• Show a "new message" indicator while being in the call #5534
• Sync group members with conversation participants #4810
• Add an option to reply privately #4855
• Conversation TopBar with icon, name and description #5596

⚙️ Changed

• Use all defined STUN and TURN servers instead of a random one #5503 #5491
• Compatibility with Nextcloud 22

🐞 Fixed

• Allow to mention groupfolder users in file chats #4246
• Fix not sending signaling messages to participants without a Peer object #4686
• Fix several issues with video, stream and screenshare selections

🏁 Removed

• Conversations API v1, v2 and v3
• Call API v1, v2 and v3
• Signaling API v1 and v2
• Support for Internet Explorer

[nickvergessen]

/backport to stable22

[PVince81]

👍

I guess there might be a bit more minor fixes but we might have backported them further.