ListObjects Metadata Caching (#10648)

Design: https://gist.github.com/klauspost/025c09b48ed4a1293c917cecfabdf21c

Gist of improvements:

* Cross-server caching and listing will use the same data across servers and requests.
* Lists can be arbitrarily resumed at a constant speed.
* Metadata for all files scanned is stored for streaming retrieval.
* The existing bloom filters controlled by the crawler is used for validating caches.
* Concurrent requests for the same data (or parts of it) will not spawn additional walkers.
* Listing a subdirectory of an existing recursive cache will use the cache.
* All listing operations are fully streamable so the number of objects in a bucket no 
  longer dictates the amount of memory.
* Listings can be handled by any server within the cluster.
* Caches are cleaned up when out of date or superseded by a more recent one.

cmd/erasure-healing-common_test.go

@@ -211,7 +211,7 @@ func TestListOnlineDisks(t *testing.T) {
 				// and check if that disk
 				// appears in outDatedDisks.
 				tamperedIndex = index
-				dErr := erasureDisks[index].DeleteFile(context.Background(), bucket, pathJoin(object, fi.DataDir, "part.1"))
+				dErr := erasureDisks[index].Delete(context.Background(), bucket, pathJoin(object, fi.DataDir, "part.1"), false)
 				if dErr != nil {
 					t.Fatalf("Test %d: Failed to delete %s - %v", i+1,
 						filepath.Join(object, "part.1"), dErr)