Currently when using `unit` parameter in the `rate` aggregator in time series mode (meaning the `rate` aggregation is defined as a child aggregation of `time_series` aggregation) then this parameter is ignored. We should investigate whether this parameter can be supported for computing rate in time series mode.
x-pack/plugin/analytics/src/test/java/org/elasticsearch/xpack/analytics/rate/InternalResetTrackingRateTests.java
@Override
    protected SearchPlugin registerPlugin() {
        return new AnalyticsPlugin();
    }
    @Override
    protected InternalResetTrackingRate createTestInstance(String name, Map<String, Object> metadata) {
        return new InternalResetTrackingRate(name, null, metadata, 0, 0, 0, 0, 0);