[Workflow] Add search in variable dropdown (#8479)

- fix Icon variable Plus
- add search input 
- fix dropdown height

## Before

![image](https://github.com/user-attachments/assets/49f73efd-21cc-4ecd-a494-f51edc34dc57)


## After

![image](https://github.com/user-attachments/assets/2af2c7ee-72fd-4dae-a1ef-19e75e1ac026)

packages/twenty-front/src/modules/ui/layout/dropdown/components/DropdownMenuHeader.tsx

@@ -15,9 +15,10 @@ const StyledHeader = styled.li`
   border-top-right-radius: ${({ theme }) => theme.border.radius.sm};
   border-bottom: 1px solid ${({ theme }) => theme.border.color.light};
 
-  padding: ${({ theme }) => theme.spacing(1)};
+  padding: ${({ theme }) => theme.spacing(1)} 0;
 
   user-select: none;
+  width: inherit;
 
   &:hover {
     background: ${({ theme, onClick }) =>

packages/twenty-front/src/modules/ui/layout/dropdown/components/StyledDropdownButtonContainer.tsx

@@ -3,12 +3,17 @@ import styled from '@emotion/styled';
 type StyledDropdownButtonProps = {
   isUnfolded: boolean;
   isActive?: boolean;
+  transparentBackground?: boolean;
 };
 
 export const StyledDropdownButtonContainer = styled.div<StyledDropdownButtonProps>`
   align-items: center;
-  background: ${({ theme, isUnfolded }) =>
-    isUnfolded ? theme.background.transparent.light : theme.background.primary};
+  background: ${({ theme, isUnfolded, transparentBackground }) =>
+    transparentBackground
+      ? 'none'
+      : isUnfolded
+        ? theme.background.transparent.light
+        : theme.background.primary};
   border-radius: ${({ theme }) => theme.border.radius.sm};
   color: ${({ isActive, theme }) =>
     isActive ? theme.color.blue : theme.font.color.secondary};
@@ -22,9 +27,11 @@ export const StyledDropdownButtonContainer = styled.div<StyledDropdownButtonProp
   user-select: none;
 
   &:hover {
-    background: ${({ theme, isUnfolded }) =>
-      isUnfolded
-        ? theme.background.transparent.medium
-        : theme.background.transparent.light};
+    background: ${({ theme, isUnfolded, transparentBackground }) =>
+      transparentBackground
+        ? 'transparent'
+        : isUnfolded
+          ? theme.background.transparent.medium
+          : theme.background.transparent.light};
   }
 `;