Support deprecation of plain text sender_key and device_id in a megolm message

[BillCarsonFr]

As part of MSC3700 the sender_keyand device_id will be removed from the encrypted message content:

POC matrix-org/matrix-rust-sdk#481

• Check all impacts
  • For key requesting (use wildcard when requesting to sender)
  • Deprecate sender*key in key requests
  • Impact on auto-rs
  • Maintain a mapping of sessionid to senderkey on m.roomkey, and m.forwardedroom*key ?
• Notify other clients of impact
• IOS
• Android
• Web
• Rust

[BillCarsonFr]

Will be done in megolm v2