Button for Doctolib

Add a floating button for Doctolib with a custom link, a custom label, a custom color, and a custom position.

Features:
* Custom label
* Custom Doctolib link
* Custom button color (color picker)
* 6 positions (corners or full-width top/bottom)
* Option to open link in same tab or new tab
* Appearance delay with fade-in animation
* Option to show or hide the Doctolib logo
* Visibility control (all pages, home only, or all pages except home)
* Accessibility: aria-label on the button, aria-hidden on the decorative icon