Export bucket usage counts as part of bucket metrics (#9710)

Bonus fixes in quota enforcement to use the
new datastructure and use timedValue to cache
a value/reload automatically avoids one less
global variable.

cmd/admin-handlers-users.go

@@ -654,8 +654,8 @@ func (a adminAPIHandlers) AccountUsageInfoHandler(w http.ResponseWriter, r *http
 		if rd || wr {
 			var size uint64
 			// Fetch the data usage of the current bucket
-			if !dataUsageInfo.LastUpdate.IsZero() && len(dataUsageInfo.BucketsSizes) > 0 {
-				size = dataUsageInfo.BucketsSizes[bucket.Name]
+			if !dataUsageInfo.LastUpdate.IsZero() {
+				size = dataUsageInfo.BucketsUsage[bucket.Name].Size
 			}
 			acctInfo.Buckets = append(acctInfo.Buckets, madmin.BucketUsageInfo{
 				Name:    bucket.Name,