pageserver: filter WAL by ShardIdentity

libs/pageserver_api/src/shard.rs

@@ -411,6 +411,12 @@ impl ShardIdentity {
             String::new()
         }
     }
+
+    /// Convenience for checking if this identity is the 0th shard in a tenant,
+    /// for special cases on shard 0 such as ingesting relation sizes.
+    pub fn is_zero(&self) -> bool {
+        self.number == ShardNumber(0)
+    }
 }
 
 impl Serialize for ShardIndex {