Add an indicator for live-streamed talks

[robinlopez]

Description:

For conferences broadcast live, it would be useful to display a visible indicator on the talk cards. And in the details of the talk, a link to watch the live stream. This feature is particularly useful for remote events, as it would make it easier for participants to follow live presentations

Tasks:

• Add a visual indicator on the conference cards when the live broadcast is in progress.
• Display the viewing link directly on the talk details page.