schema: Finish converting dashboard schema datasource references to objects (#47806)

* coremodel: finish string -> object datasource ref

Seems we missed updating a couple of the datasource references from
strings to objects.

* cue fmt

* Also fix dashboard in scuemata dashboard schema

* Update devenv/dev-dashboards/panel-graph/graph-ng-stacking2.json

Co-authored-by: Ryan McKinley <ryantxu@gmail.com>

Co-authored-by: Ryan McKinley <ryantxu@gmail.com>

scripts/stripnulls.sh

@@ -7,7 +7,7 @@
 SED=$(command -v gsed)
 SED=${SED:-"sed"}
 
-FILES=$(grep -rl '"schemaVersion": 3[34]' devenv)
+FILES=$(grep -rl '"schemaVersion": 3[3456]' devenv)
 set -e
 set -x
 for DASH in ${FILES}; do echo "${DASH}"; grep -v 'null,$' "${DASH}" > "${DASH}-nulless"; mv "${DASH}-nulless" "${DASH}"; done