Cosmos: Honor ValueGenerated

[AndriySvyryd]

It would set EnableContentResponseOnWrite = true and read the new value from the response.
It would also avoid setting a property if it is currently assigned the default value.

[ajcvickers]

@AndriySvyryd In what way is ValueGenerated not currently honored by the Cosmos provider?

[AndriySvyryd]

Cosmos doesn't call GetBeforeSaveBehavior() and GetAfterSaveBehavior() to determine how a given property should be handled.