storage scrubber: GC ancestor shard layers (#8196)

## Problem

After a shard split, the pageserver leaves the ancestor shard's content
in place. It may be referenced by child shards, but eventually child
shards will de-reference most ancestor layers as they write their own
data and do GC. We would like to eventually clean up those ancestor
layers to reclaim space.

## Summary of changes

- Extend the physical GC command with `--mode=full`, which includes
cleaning up unreferenced ancestor shard layers
- Add test `test_scrubber_physical_gc_ancestors`
- Remove colored log output: in testing this is irritating ANSI code
spam in logs, and in interactive use doesn't add much.
- Refactor storage controller API client code out of storcon_client into
a `storage_controller/client` crate
- During physical GC of ancestors, call into the storage controller to
check that the latest shards seen in S3 reflect the latest state of the
tenant, and there is no shard split in progress.

storage_controller/src/main.rs

@@ -5,6 +5,7 @@ use metrics::launch_timestamp::LaunchTimestamp;
 use metrics::BuildInfo;
 use std::path::PathBuf;
 use std::sync::Arc;
+use std::time::Duration;
 use storage_controller::http::make_router;
 use storage_controller::metrics::preinitialize_metrics;
 use storage_controller::persistence::Persistence;
@@ -310,12 +311,21 @@ async fn async_main() -> anyhow::Result<()> {
     tracing::info!("Terminating on signal");
 
     // Stop HTTP server first, so that we don't have to service requests
-    // while shutting down Service
+    // while shutting down Service.
     server_shutdown.cancel();
-    if let Err(e) = server_task.await {
-        tracing::error!("Error joining HTTP server task: {e}")
+    match tokio::time::timeout(Duration::from_secs(5), server_task).await {
+        Ok(Ok(_)) => {
+            tracing::info!("Joined HTTP server task");
+        }
+        Ok(Err(e)) => {
+            tracing::error!("Error joining HTTP server task: {e}")
+        }
+        Err(_) => {
+            tracing::warn!("Timed out joining HTTP server task");
+            // We will fall through and shut down the service anyway, any request handlers
+            // in flight will experience cancellation & their clients will see a torn connection.
+        }
     }
-    tracing::info!("Joined HTTP server task");
 
     service.shutdown().await;
     tracing::info!("Service shutdown complete");