safekeeper: make timeline deletions a bit more verbose (#10721)

Make timeline deletion print the sub-steps, so that we can narrow down
some stuck timeline deletion issues we are observing.

https://neondb.slack.com/archives/C08C2G15M6U/p1738930694716009

safekeeper/src/timeline.rs

@@ -592,6 +592,8 @@ impl Timeline {
         assert!(self.cancel.is_cancelled());
         assert!(self.gate.close_complete());
 
+        info!("deleting timeline {} from disk", self.ttid);
+
         // Close associated FDs. Nobody will be able to touch timeline data once
         // it is cancelled, so WAL storage won't be opened again.
         shared_state.sk.close_wal_store();

safekeeper/src/timelines_global_map.rs

@@ -475,6 +475,8 @@ impl GlobalTimelines {
                 info!("deleting timeline {}, only_local={}", ttid, only_local);
                 timeline.shutdown().await;
 
+                info!("timeline {ttid} shut down for deletion");
+
                 // Take a lock and finish the deletion holding this mutex.
                 let mut shared_state = timeline.write_shared_state().await;