DifferenceStringSet returns the elements that are present in `b`, but not in `a`.

IsConfigUpdatingAt checks whether the attribute given by the Path is not Equal() between plan and state.

SetFlagImporting checks the respDiags and if they are error-free it sets the `importing` as a private flag inside SetKeyer.

SetGjson conveniently wraps sjson.SetRaw, so that it acts on gjson.Result directly.

ToLower is the same as strings.ToLower, except it cares to not to convert null/unknown strings into empty strings.

SetKeyer is something like ReadResponse.Private or ImportStateResponse.Private.