Markdown preview image rendering (#21082)

Closes https://github.com/zed-industries/zed/issues/13246

Supersedes: https://github.com/zed-industries/zed/pull/16192

I couldn't push to the git fork this user was using, so here's the exact
same PR but with some style nits implemented.


Release Notes:

- Added image rendering to the Markdown preview

---------

Co-authored-by: dovakin0007 <dovakin0007@gmail.com>
Co-authored-by: dovakin0007 <73059450+dovakin0007@users.noreply.github.com>

crates/notifications/src/notification_store.rs

@@ -238,11 +238,8 @@ impl NotificationStore {
     ) -> Result<()> {
         this.update(&mut cx, |this, cx| {
             if let Some(notification) = envelope.payload.notification {
-                if let Some(rpc::Notification::ChannelMessageMention {
-                    message_id,
-                    sender_id: _,
-                    channel_id: _,
-                }) = Notification::from_proto(&notification)
+                if let Some(rpc::Notification::ChannelMessageMention { message_id, .. }) =
+                    Notification::from_proto(&notification)
                 {
                     let fetch_message_task = this.channel_store.update(cx, |this, cx| {
                         this.fetch_channel_messages(vec![message_id], cx)