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/rpc.rs

@@ -3396,6 +3396,9 @@ fn build_channels_update(
     for channel in channel_invites {
         update.channel_invitations.push(channel.to_proto());
     }
+    for project in channels.hosted_projects {
+        update.hosted_projects.push(project);
+    }
 
     update
 }