[Chore] update to cue v0.4.0 (#39641)

* change global flag to flagset

* update pr with comments

* replace flag.args by flagset

* fix build

* migrate the schema package to use cue 4.0

* fix the load package

pkg/schema/load/common.go

@@ -6,12 +6,12 @@ import (
 	"io/fs"
 	"path/filepath"
 
-	"cuelang.org/go/cue"
+	"cuelang.org/go/cue/cuecontext"
 	"cuelang.org/go/cue/load"
 	"github.com/grafana/grafana"
 )
 
-var rt = &cue.Runtime{}
+var ctx = cuecontext.New()
 
 // Families can have variants, where more typing information narrows the
 // possible values for certain keys in schemas. These are a meta-property