Room-level default Sender Display property

**Description:**

Please note, this is Matrix specification extend proposal.

Currently Matrix client (eg. Element) displays the message sender by default. This too restrictive and in some cases unnecessary and ugly. You do not always need to know the sender, eg. when bots send messages to a room.

In LinkedIn or Facebook page, do not show which page admin/moderator or bot send the message. No one is interested to know that. What people interested to know is that there is a new message in the room/channel or page.

Therefore, I propose a room-level default Sender Display property (hypothetically named defaultSenderDisplay).

The defaultSenderDisplay by default is true. That is client display the message sender.

If room admin sets defaultSenderDisplay to false, client does not display the message sender for the room.

Start by reviewing the Matrix specification and its extension proposal process to identify where a room-level property would be defined. Confirm how the proposed defaultSenderDisplay behavior should be represented and documented, including the default value and client behavior; no file or test is named in the issue.

Written by the indexing model from the issue text.