Extend msgtype m.text properties to control the URL preview

[wmwsagara]

Description:

Please note, this is Matrix specification extend proposal.
Referring to: https://spec.matrix.org/v1.5/client-server-api/#mtext

URL preview is desired but not always require for all messages in a room where automatic URL preview is enabled.

Example, certain types of bot messages do not require URL previews.

Automatic URL preview on messages where URL preview is not applicable, makes those messages too blot, ugly and difficult to read fast.

I propose a message-level url preview control property, hypothetically named displayUrlPreview, where message sender control the URL preview.

If the URL preview is enabled for a room, and:

1. If displayUrlPreview is true for the message, then client should render the URL preview.
2. If displayUrlPreview is false for the message, then client should not render the URL preview.

If the URL preview is NOT enabled for a room:
3. Regardless of displayUrlPreview is true or false for the message, client should not render the URL preview.

[turt2live]

Duplicate of #221