storage controller: fixes to secondary location handling (#7169)

Stacks on:
- https://github.com/neondatabase/neon/pull/7165

Fixes while working on background optimization of scheduling after a
split:
- When a tenant has secondary locations, we weren't detaching the parent
shards' secondary locations when doing a split
- When a reconciler detaches a location, it was feeding back a
locationconf with `Detached` mode in its `observed` object, whereas it
should omit that location. This could cause the background reconcile
task to keep kicking off no-op reconcilers forever (harmless but
annoying).
- During shard split, we were scheduling secondary locations for the
child shards, but no reconcile was run for these until the next time the
background reconcile task ran. Creating these ASAP is useful, because
they'll be used shortly after a shard split as the destination locations
for migrating the new shards to different nodes.

pageserver/src/tenant/secondary/downloader.rs

@@ -11,6 +11,7 @@ use crate::{
     disk_usage_eviction_task::{
         finite_f32, DiskUsageEvictionInfo, EvictionCandidate, EvictionLayer, EvictionSecondaryLayer,
     },
+    is_temporary,
     metrics::SECONDARY_MODE,
     tenant::{
         config::SecondaryLocationConfig,
@@ -961,7 +962,10 @@ async fn init_timeline_state(
             // Secondary mode doesn't use local metadata files, but they might have been left behind by an attached tenant.
             warn!(path=?dentry.path(), "found legacy metadata file, these should have been removed in load_tenant_config");
             continue;
-        } else if crate::is_temporary(&file_path) || is_temp_download_file(&file_path) {
+        } else if crate::is_temporary(&file_path)
+            || is_temp_download_file(&file_path)
+            || is_temporary(&file_path)
+        {
             // Temporary files are frequently left behind from restarting during downloads
             tracing::info!("Cleaning up temporary file {file_path}");
             if let Err(e) = tokio::fs::remove_file(&file_path)