Set X-Cache and X-Cache-Lookup headers for cache (#8794)

X-Cache sets cache status of HIT if object is
served from the disk cache, or MISS otherwise.
X-Cache-Lookup is set to HIT if object was found
in the cache even if not served (for e.g. if cache
 entry was invalidated by ETag verification)

cmd/disk-cache-backend.go

@@ -89,8 +89,10 @@ func (m *cacheMeta) ToObjectInfo(bucket, object string) (o ObjectInfo) {
 	}
 
 	o = ObjectInfo{
-		Bucket: bucket,
-		Name:   object,
+		Bucket:            bucket,
+		Name:              object,
+		CacheStatus:       CacheHit,
+		CacheLookupStatus: CacheHit,
 	}
 
 	// We set file info only if its valid.