feat(datetime-picker): set material_green theme to flatpickr

upgrade docker dev's php version to 8.1

app/Resources/js/modules/DateTimePicker.ts

 import flatpickr from "flatpickr";
 import "flatpickr/dist/flatpickr.min.css";
+import "flatpickr/dist/themes/material_green.css";
 
 /*
  * Detects navigator locale 24h time preference

docker/development/Dockerfile

@@ -4,7 +4,7 @@
 # ⚠️ NOT optimized for production
 # should be used only for development purposes
 #---------------------------------------------------
-FROM php:8.0-fpm
+FROM php:8.1-fpm
 
 LABEL maintainer="Yassine Doghri <yassine@doghri.fr>"