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/xl-storage.go

@@ -632,7 +632,7 @@ func (s *xlStorage) NSScanner(ctx context.Context, cache dataUsageCache, updates
 		for _, freeVersion := range fivs.FreeVersions {
 			oi := freeVersion.ToObjectInfo(item.bucket, item.objectPath(), versioned)
 			done = globalScannerMetrics.time(scannerMetricTierObjSweep)
-			item.applyTierObjSweep(ctx, objAPI, oi)
+			globalExpiryState.enqueueFreeVersion(oi)
 			done()
 		}