Refactor: use chunk manager to manage resume upload in server side

pkg/filesystem/chunk/backoff/backoff.go

@@ -0,0 +1,31 @@
+package backoff
+
+import "time"
+
+// Backoff used for retry sleep backoff
+type Backoff interface {
+	Next() bool
+	Reset()
+}
+
+// ConstantBackoff implements Backoff interface with constant sleep time
+type ConstantBackoff struct {
+	Sleep time.Duration
+	Max   int
+
+	tried int
+}
+
+func (c *ConstantBackoff) Next() bool {
+	c.tried++
+	if c.tried >= c.Max {
+		return false
+	}
+
+	time.Sleep(c.Sleep)
+	return true
+}
+
+func (c *ConstantBackoff) Reset() {
+	c.tried = 0
+}