Add thread info to EventTile

[germain-gg]

Above is a low fidelity version of what this should look like
Make the UI reactive so that every new message updates the event tile and displays the number of replies in the thread.

The label "1 new" is out of scope for this iteration as we are leaving read receipts out for now to focus on more critical part of the experience

[janogarcia]

@gsouquet I'll be sharing a few variants today for the thread preview tile. We may need to add some extra bits of information, other than the reply count, but it's OK to leave the new message count out for this iteration.

[germain-gg]

Duplicate of #18958