storcon: log all safekeepers marked as offline (#10898)

Doing this to help debugging offline safekeepers.

Part of https://github.com/neondatabase/neon/issues/9011

storage_controller/src/heartbeater.rs

@@ -346,7 +346,13 @@ impl HeartBeat<Safekeeper, SafekeeperState> for HeartbeaterTask<Safekeeper, Safe
                             // We ignore the node in this case.
                             return None;
                         }
-                        Err(_) => SafekeeperState::Offline,
+                        Err(e) => {
+                            tracing::info!(
+                                "Marking safekeeper {} at as offline: {e}",
+                                sk.base_url()
+                            );
+                            SafekeeperState::Offline
+                        }
                     };
 
                     Some((*node_id, status))

storage_controller/src/safekeeper.rs

@@ -112,7 +112,7 @@ impl Safekeeper {
             warn_threshold,
             max_retries,
             &format!(
-                "Call to node {} ({}:{}) management API",
+                "Call to safekeeper {} ({}:{}) management API",
                 self.id, self.listen_http_addr, self.listen_http_port
             ),
             cancel,