Customizable zIndex on Bubble component

[baptisteArno]

Originate from #878

In the EU, we are required to set a cookie banner when a visitor first visits a website. This cookie banner should have the upper most priority in terms of visibility. When trying to assign the typebot script a lower zIndex than the cookie banner, it still always manages to appear on top. I assume this is part of the script. This results in the bubble and preview message to appear on top of the cookie banner buttons (accept, deny, settings) on mobile and is problematic.