Add rich update support to store/v2 Interface

[c-kruse]

The store/v2 interface does not provide an efficient way for callers to know if a resource was created, updated or not modified.

Feature Suggestion

Extend the store/v2 interface to allow for this information to be communicated. Consideration should given to how this interface should function. Options discussed so far are either providing the caller with a status indicating the action taken or providing the caller with the previous value when available for them to make the WasModified call.

Context

In order to deliver #4341, there will need to be a store api that supports it.

The choice to only make this change in the store v2 interface rather than in both or just the store interface (v1) is influenced by plans to add a postgres store implementation #4615.

[calebhailey]

Related: #4609