Add support for Downsampling in ES|QL

[limotova]

Subtasks:

• Support aggregations on aggregate_metric_double Add support for non-grouping aggregations on aggregate_metric_double field in es|ql #110649 [ES|QL] Support some stats on aggregate_metric_double #120343
• Support grouping aggregations on aggregate_metric_doubleAdd support for non-grouping aggregations on aggregate_metric_double field in es|ql #110649 (yaml tests in [ES|QL] Support subset of metrics in agg metric double #121805)
• Handle configuration of a subset of metrics in aggregate_metric_double field (for example, only min and max) [ES|QL] Support subset of metrics in agg metric double #121805
• Rendering aggregate_metric_double values (i.e. from table | keep agg_metric). [ES|QL] Render aggregate_metric_double #122660
• Support reading from normal index and downsampled index at the same time (so aggregate metric double is the field type in the latter, and the former is the original numeric type) [ES|QL] ToAggregateMetricDouble function #124595 [ES|QL] Add ToAggregateMetricDouble example #125518
• Support sorting on aggregate_metric_double Not supporting, but PR to fix sorting when aggregate_metric_double is present: [ES|QL] Fix sorting when aggregate_metric_double present #125191
• Introduce enum to CompositeBlock to distinguish between different usages of CompositeBlock Use AggregateMetricDoubleBlock instead of CompositeBlock [ES|QL] Introduce AggregateMetricDoubleBlock #127299
• Investigate handling to_aggregate_metric_double_conversions automatically/without the need of an explicit convert function Report suggested_types if no convert function is provided [ES|QL] Add suggested_cast #127139
• Convert to aggregate_metric_double implicitly in aggregations (max, min, sum, count) where aggregate_metric_doubles are passed in
• Maybe render individual sub-metrics from aggregate_metric_double Expose FROM_AGGREGATE_METRIC_DOUBLE function
• Improve handling of valueCount-related methods in CompositeBlock
• Support other aggregations (using default metric?)
• Add support for _doc_count field
• Investigate handling accuracy loss (if original pre-downsampled field was a whole number vs double)
• Add aggregate_metric_double to benchmarks

[elasticsearchmachine]

Pinging @elastic/es-storage-engine (Team:StorageEngine)

[elasticsearchmachine]

Pinging @elastic/es-analytical-engine (Team:Analytics)