Flow aggregation - alternate indices based on duration of time range filter

In order to leverage pre-aggregated metrics we would like update the search queries in the ElasticFlowRepository to use alternate indices based on the duration of the time range filter.

To do this let's define new properties called timeRangeAggregateThresholdMs (defaults to 0) and aggregateIndexPrefix (defaults to 'aggregated-flows'). When timeRangeAggregateThresholdMs is set to a value greater than 0 and the duration of the timestamp in the given query exceeds this value then we should use aggregateIndexPrefix as the index prefix instead of indexPrefix.