Replace node-sass with sass and update bootstrap to version 5.3

webpack.config.js

@@ -74,7 +74,12 @@ module.exports = (async () => {
   // basic encore configuration
   Encore.setOutputPath("public/build/")
     .setPublicPath("/build")
-    .enableSassLoader()
+    .enableSassLoader(function (options) {
+      // If set to true, Sass won’t print warnings that are caused by dependencies (like bootstrap):
+      // https://sass-lang.com/documentation/js-api/interfaces/options/#quietDeps
+        options.sassOptions.quietDeps = true;
+        options.sassOptions.silenceDeprecations = ['import'];
+    })
     .enableVueLoader(() => {}, {
       version: 3,
     })