The metric kind of the time series. When listing time series, this metric kind might be different from the metric kind of the associated metric if this time series is an alignment or reduction of other time series.
When creating a time series, this field is optional. If present, it must be the same as the metric kind of the associated metric. If the associated metric's descriptor must be auto-created, then this field specifies the metric kind of the new descriptor and must be either GAUGE (the default) or CUMULATIVE.
We have this validation: https://github.com/googleinterns/cloud-operations-api-mock/blob/e8bcc34f971a612c9e598ce4c66c192448c7dac6/internal/validation/mock_metric_validation.go#L344-L356
However, the GCM documentation says: