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* Caches are cleaned up when out of date or superseded by a more recent one.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/fs-v1-helpers_test.go

@@ -297,7 +297,7 @@ func TestFSDeletes(t *testing.T) {
 			srcPath:     "success-file",
 			expectedErr: nil,
 		},
-		// The file was deleted in the last case, so DeleteFile should fail.
+		// The file was deleted in the last case, so Delete should fail.
 		{
 			basePath:    path,
 			srcVol:      "success-vol",
@@ -423,7 +423,7 @@ func TestFSRemoves(t *testing.T) {
 			expectedErr: nil,
 		},
 		// Test case - 2.
-		// The file was deleted in the last case, so DeleteFile should fail.
+		// The file was deleted in the last case, so Delete should fail.
 		{
 			srcFSPath:   path,
 			srcVol:      "success-vol",