osbuild2: add Users and Groups to kickstart stage

Supported by the osbuild stage for a while now.

internal/osbuild2/kickstart_stage.go

@@ -7,6 +7,10 @@ type KickstartStageOptions struct {
 	OSTree *OSTreeOptions `json:"ostree,omitempty"`
 
 	LiveIMG *LiveIMG `json:"liveimg,omitempty"`
+
+	Users map[string]UsersStageOptionsUser `json:"users,omitempty"`
+
+	Groups map[string]GroupsStageOptionsGroup `json:"groups,omitempty"`
 }
 
 type LiveIMG struct {