ssh remoting: Show the host's GitHub name in the titlebar when sharing an SSH project (#19844)

The name (GitHub name) of the host was not displayed when sharing an ssh
project.

Previously we assumed that the a collaborator is a host if the
`replica_id` of the collaborator was `0`,
but for ssh project the `replica_id` is actually `1`.

<img width="329" alt="Screenshot 2024-10-28 at 18 16 30"
src="https://github.com/user-attachments/assets/c0151e12-a96f-4f38-aec1-4ed5475a9eaf">


Co-Authored-by: Thorsten <thorsten@zed.dev>

Release Notes:

- N/A

---------

Co-authored-by: Thorsten <thorsten@zed.dev>

crates/proto/proto/zed.proto

@@ -1721,6 +1721,7 @@ message Collaborator {
     PeerId peer_id = 1;
     uint32 replica_id = 2;
     uint64 user_id = 3;
+    bool is_host = 4;
 }
 
 message User {