Improve expiration of tiered objects (#18926)

- Use a shared worker pool for all ILM expiry tasks
- Free version cleanup executes in a separate goroutine
- Add a free version only if removing the remote object fails
- Add ILM expiry metrics to the node namespace
- Move tier journal tasks to expiryState
- Remove unused on-disk journal for tiered objects pending deletion
- Distribute expiry tasks across workers such that the expiry of versions of
  the same object serialized
- Ability to resize worker pool without server restart
- Make scaling down of expiryState workers' concurrency safe; Thanks
  @klauspost
- Add error logs when expiryState and transition state are not
  initialized (yet)
* metrics: Add missed tier journal entry tasks
* Initialize the ILM worker pool after the object layer

cmd/erasure-metadata_test.go

@@ -314,3 +314,11 @@ func TestTransitionInfoEquals(t *testing.T) {
 		t.Fatalf("Expected to be inequal: fi %v ofi %v", fi, ofi)
 	}
 }
+
+func TestSkipTierFreeVersion(t *testing.T) {
+	fi := newFileInfo("object", 8, 8)
+	fi.SetSkipTierFreeVersion()
+	if ok := fi.SkipTierFreeVersion(); !ok {
+		t.Fatal("Expected SkipTierFreeVersion to be set on FileInfo but wasn't")
+	}
+}