965 flow control arrow menu 1/3 add insert step button (#12519)

Add insert step button to workflow edges



https://github.com/user-attachments/assets/7144f722-f1c7-450f-a8eb-c902071986a1



Also fixes `iconButtonGroup` UI component

## Before


https://github.com/user-attachments/assets/7b5f0245-d0e8-48af-9aa5-a29388a1caea


## After



https://github.com/user-attachments/assets/1820874f-aa99-41ae-8254-c76c275ee3ae

packages/twenty-front/src/modules/settings/data-model/graph-overview/components/SettingsDataModelOverview.tsx

@@ -204,8 +204,7 @@ export const SettingsDataModelOverview = () => {
       >
         <Background />
         <IconButtonGroup
-          className="react-flow__panel react-flow__controls bottom left"
-          size="small"
+          className="react-flow__panel react-flow__controls bottom left horizontal"
           iconButtons={[
             {
               Icon: IconPlus,