Dashboards: Remove default empty string from variable create view (#98922)

* default empty string

* optimize

e2e/dashboards-suite/new-query-variable.spec.ts

@@ -72,7 +72,7 @@ describe('Variables - Query - Add variable', () => {
       cy.get('input[type="checkbox"]').should('not.be.checked');
     });
 
-    e2e.pages.Dashboard.Settings.Variables.Edit.General.previewOfValuesOption().should('not.have.text');
+    e2e.pages.Dashboard.Settings.Variables.Edit.General.previewOfValuesOption().should('not.exist');
     e2e.pages.Dashboard.Settings.Variables.Edit.General.selectionOptionsCustomAllInput().should('not.exist');
   });
 

public/app/features/dashboard-scene/settings/variables/VariableEditorForm.tsx

@@ -113,7 +113,7 @@ export function VariableEditorForm({
 
       {EditorToRender && <EditorToRender variable={variable} onRunQuery={onRunQuery} />}
 
-      {isHasVariableOptions && <VariableValuesPreview options={variable.getOptionsForSelect()} />}
+      {isHasVariableOptions && <VariableValuesPreview options={variable.getOptionsForSelect(false)} />}
 
       <div className={styles.buttonContainer}>
         <Stack gap={2}>