GroupBy variable core integration (#82185)

* Bump scenes

* Make GroupByVariableModel a VariableWithOptions

* Serialise/deserialise group by variable

* WIP: Group by variable editor

* WIP tests

* Group by variable tests

* add feature toggle and gate variable creation behind it

* Fix types

* Do not resolve DS variable

* Do not show the message if no DS is selected

* Now groupby has options and current

* Update public/app/features/dashboard-scene/settings/variables/components/GroupByVariableForm.test.tsx

Co-authored-by: Ivan Ortega Alba <ivanortegaalba@gmail.com>

* don't allow creating groupby if toggle is off + update tests

* add unit tests

* remove groupByKeys

---------

Co-authored-by: Ashley Harrison <ashley.harrison@grafana.com>
Co-authored-by: Ivan Ortega <ivanortegaalba@gmail.com>

pkg/services/featuremgmt/toggles_gen.go

@@ -658,4 +658,8 @@ const (
 	// FlagKubernetesAggregator
 	// Enable grafana aggregator
 	FlagKubernetesAggregator = "kubernetesAggregator"
+
+	// FlagGroupByVariable
+	// Enable groupBy variable support in scenes dashboards
+	FlagGroupByVariable = "groupByVariable"
 )