feat: Add stock strings for being added/removed from group (#8562)

Adds following stock strings:
- You were removed by %1$s.
- You were added by %1$s.

and implicit equivalents:
- You were removed.
- You were added.

Closes: #8419

Signed-off-by: Jagoda Ślązak <jslazak@jslazak.com>

src/sync.rs

@@ -810,7 +810,7 @@ mod tests {
         let fiona = &tcm.fiona().await;
         tcm.exec_securejoin_qr(fiona, alice2, &qr).await;
         let msg = fiona.get_last_msg().await;
-        assert_eq!(msg.text, "Member Me added by alice@example.org.");
+        assert_eq!(msg.text, "You were added by alice@example.org.");
         Ok(())
     }