GroupBy: add new groupby variable type and optional groupByKeys (#81717)

* add new groupby type

* rename to groupByKeys + introduce GroupByVariableModel

* fix unit test

* update scenes package

* update interface

* update fixture

* update unit test

* bump to scenes 2.6.2

* remove baseFilters for now

package.json

@@ -246,7 +246,7 @@
     "@grafana/o11y-ds-frontend": "workspace:*",
     "@grafana/prometheus": "workspace:*",
     "@grafana/runtime": "workspace:*",
-    "@grafana/scenes": "^2.4.0",
+    "@grafana/scenes": "2.6.3",
     "@grafana/schema": "workspace:*",
     "@grafana/sql": "workspace:*",
     "@grafana/ui": "workspace:*",