Storybook fix dark mode (#4865)

preview has now also a dark background & added a one click change theme
button

<img width="994" alt="Bildschirmfoto 2024-04-06 um 18 27 45"
src="https://github.com/twentyhq/twenty/assets/48770548/95f12617-e48f-4492-9b51-13410aff43ee">

packages/twenty-front/.storybook/manager-head.html

@@ -0,0 +1,5 @@
+<style>
+    [data-is-storybook="true"] {
+        background-color: transparent!important;
+    }
+</style>