Need to add a property to indicate last modified time for the entries in the Keyspace

[yahoNanJing]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

To better classify and manage the entries in the Keyspace, it's better to add a property to indicate the last modified time for each entry. For those one with an old last modified time, we can delete them or move them to a historical storage.

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