Implement attributes to ignore certain properties for `DataModel`

[greymistcube]

Currently as implemented in #1935, DataModel.Encod() encodes all public properties. This may not be desirable in all cases and probably hampers with data modeling where one might want a public property that is not part of a stored data. An attribute such as [IgnoreProperty] to ignore a property when encoding might be useful.

[stale[bot]]

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