Add `date` value type support for certain metrics in Rollup

[benwtrent]

Currently, when creating a new RollupJobConfig only numeric field mapper types are supported for the different metrics.

Support for min, max and, value_count over date fields should be added. Since date can just be treated as a long, hopefully the change is not too pervasive.

This issue is blocking ML support for rollup indices: #31999

Pinging @colings86 @polyfractal

[elasticmachine]

Pinging @elastic/es-search-aggs