do not panic on rebalance during server restarts (#19563)

This PR makes a feasible approach to handle all the scenarios
that we must face to avoid returning "panic."

Instead, we must return "errServerNotInitialized" when a
bucketMetadataSys.Get() is called, allowing the caller to
retry their operation and wait.

Bonus fix the way data-usage-cache stores the object.
Instead of storing usage-cache.bin with the bucket as
`.minio.sys/buckets`, the `buckets` must be relative
to the bucket `.minio.sys` as part of the object name.

Otherwise, there is no way to decommission entries at
`.minio.sys/buckets` and their final erasure set positions.

A bucket must never have a `/` in it. Adds code to read()
from existing data-usage.bin upon upgrade.

cmd/erasure-object.go

@@ -1833,9 +1833,18 @@ func (er erasureObjects) DeleteObject(ctx context.Context, bucket, object string
 	var replcfg *replication.Config
 	if opts.Expiration.Expire {
 		// Check if the current bucket has a configured lifecycle policy
-		lc, _ = globalLifecycleSys.Get(bucket)
-		rcfg, _ = globalBucketObjectLockSys.Get(bucket)
-		replcfg, _ = getReplicationConfig(ctx, bucket)
+		lc, err = globalLifecycleSys.Get(bucket)
+		if err != nil && !errors.Is(err, BucketLifecycleNotFound{Bucket: bucket}) {
+			return objInfo, err
+		}
+		rcfg, err = globalBucketObjectLockSys.Get(bucket)
+		if err != nil {
+			return objInfo, err
+		}
+		replcfg, err = getReplicationConfig(ctx, bucket)
+		if err != nil {
+			return objInfo, err
+		}
 	}
 
 	// expiration attempted on a bucket with no lifecycle