[Improvement] provide a clear definition for system behavior to expand a volume to the upper limitation which defined by the IaSS

[leon-inf]

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[leon-inf]

#3163 - a related issue.

[leon-inf]

Without the definition, there is no a well-defined reasonable expectation, we can't write automated system test cases for these scenarios.

[ruijun2002]

As discussed, the limitation of a db cluster storage size is greater than 20GiB and less than 10TiB, include 20GiB and 10TiB. refer to #3642