* Elasticsearch: Add Moving Function Pipeline Aggregation

* Removing support for moving average in 7.x

* Fixing getMetricAggTypes to handle undefined esVersion

* Adding moving_fn to go code

* Update public/app/plugins/datasource/elasticsearch/metric_agg.ts

Co-authored-by: Giordano Ricci <grdnricci@gmail.com>

* Adding test for esversion 70

* Removing default value for script, adding placeholder instead

* Fixing formatting

* Adding code for handling missing or obsolete aggregations

Co-authored-by: Giordano Ricci <grdnricci@gmail.com>