Add docs for new CollectorCleaningInterval options.

Author: yang-xiaodong

docs/content/user-guide/en/cap/configuration.md

@@ -85,11 +85,17 @@ During the message sending process if consumption method fails, CAP will try to
     By default if failure occurs on send or consume, retry will start after **4 minutes** in order to avoid possible problems caused by setting message state delays.    
     Failures in the process of sending and consuming messages will be retried 3 times immediately, and will be retried polling after 3 times, at which point the FailedRetryInterval configuration will take effect.
 
+### CollectorCleaningInterval
+
+> Default: 300 sec
+
+The interval of the collector processor deletes expired messages.
+
 #### ConsumerThreadCount 
 
 > Default : 1
 
-Number of consumer threads, when this value is greater than 1, the order of message execution cannot be guaranteed
+Number of consumer threads, when this value is greater than 1, the order of message execution cannot be guaranteed.
 
 #### FailedRetryCount
 

docs/content/user-guide/zh/cap/configuration.md

@@ -92,6 +92,12 @@ services.AddCap(config =>
 
 消费者线程并行处理消息的线程数，当这个值大于1时，将不能保证消息执行的顺序。
 
+### CollectorCleaningInterval
+
+默认值：300 秒
+
+收集器删除已经过期消息的时间间隔。
+
 #### FailedRetryCount
 
 默认值：50