channel projects (#8456)

Add plumbing for hosted projects. This will currently show them if they
exist
but provides no UX to create/rename/delete them.

Also changed the `ChannelId` type to not auto-cast to u64; this avoids
type
confusion if you have multiple id types.


Release Notes:

- N/A

crates/collab/src/tests/channel_message_tests.rs

@@ -100,13 +100,13 @@ async fn test_basic_channel_messages(
             Notification::ChannelMessageMention {
                 message_id,
                 sender_id: client_a.id(),
-                channel_id,
+                channel_id: channel_id.0,
             }
         );
         assert_eq!(
             store.notification_at(1).unwrap().notification,
             Notification::ChannelInvitation {
-                channel_id,
+                channel_id: channel_id.0,
                 channel_name: "the-channel".to_string(),
                 inviter_id: client_a.id()
             }