storcon: send heartbeats concurrently (#10954)

## Problem

While looking at logs I noticed that heartbeats are sent sequentially.
The loop polling the UnorderedSet is at the wrong level of identation.
Instead of doing it after we have the full set, we did after each entry.

## Summary of Changes

Poll the UnorderedSet properly.

storage_controller/src/heartbeater.rs

@@ -223,21 +223,21 @@ impl HeartBeat<Node, PageserverState> for HeartbeaterTask<Node, PageserverState>
                     Some((*node_id, status))
                 }
             });
+        }
 
-            loop {
-                let maybe_status = tokio::select! {
-                    next = heartbeat_futs.next() => {
-                        match next {
-                            Some(result) => result,
-                            None => { break; }
-                        }
-                    },
-                    _ = self.cancel.cancelled() => { return Err(HeartbeaterError::Cancel); }
-                };
+        loop {
+            let maybe_status = tokio::select! {
+                next = heartbeat_futs.next() => {
+                    match next {
+                        Some(result) => result,
+                        None => { break; }
+                    }
+                },
+                _ = self.cancel.cancelled() => { return Err(HeartbeaterError::Cancel); }
+            };
 
-                if let Some((node_id, status)) = maybe_status {
-                    new_state.insert(node_id, status);
-                }
+            if let Some((node_id, status)) = maybe_status {
+                new_state.insert(node_id, status);
             }
         }
 
@@ -363,21 +363,21 @@ impl HeartBeat<Safekeeper, SafekeeperState> for HeartbeaterTask<Safekeeper, Safe
                     Some((*node_id, status))
                 }
             });
+        }
 
-            loop {
-                let maybe_status = tokio::select! {
-                    next = heartbeat_futs.next() => {
-                        match next {
-                            Some(result) => result,
-                            None => { break; }
-                        }
-                    },
-                    _ = self.cancel.cancelled() => { return Err(HeartbeaterError::Cancel); }
-                };
+        loop {
+            let maybe_status = tokio::select! {
+                next = heartbeat_futs.next() => {
+                    match next {
+                        Some(result) => result,
+                        None => { break; }
+                    }
+                },
+                _ = self.cancel.cancelled() => { return Err(HeartbeaterError::Cancel); }
+            };
 
-                if let Some((node_id, status)) = maybe_status {
-                    new_state.insert(node_id, status);
-                }
+            if let Some((node_id, status)) = maybe_status {
+                new_state.insert(node_id, status);
             }
         }