feat(curriculum): add theme switcher lab (freeCodeCamp#61404)

Co-authored-by: Dario <[email protected]>
Co-authored-by: Oliver Eyton-Williams <[email protected]>
Co-authored-by: Ilenia <[email protected]>

Author: 4 people

client/i18n/locales/english/intro.json

@@ -3529,6 +3529,12 @@
           "This will provide you with the opportunity to practice working with <code>aria-live</code> attribute."
         ]
       },
+      "lab-theme-switcher": {
+        "title": "Build a Theme Switcher",
+        "intro": [
+          "In this lab, you will build a theme switcher and practice working with the <code>aria-haspopup</code>, <code>aria-expanded</code>, and <code>aria-controls</code> attributes."
+        ]
+      },
       "review-js-a11y": {
         "title": "JavaScript and Accessibility Review",
         "intro": [

client/src/pages/learn/full-stack-developer/lab-theme-switcher/index.md

@@ -0,0 +1,9 @@
+---
+title: Introduction to the Build a Theme Switcher
+block: lab-theme-switcher
+superBlock: full-stack-developer
+---
+
+## Introduction to the Build a Theme Switcher
+
+In this lab, you will build a theme switcher and practice working with the `aria-haspopup`, `aria-expanded`, and `aria-controls` attributes.

curriculum/challenges/_meta/lab-theme-switcher/meta.json

@@ -0,0 +1,11 @@
+{
+  "name": "Build a Theme Switcher",
+  "isUpcomingChange": true,
+  "blockType": "lab",
+  "blockLayout": "link",
+  "dashedName": "lab-theme-switcher",
+  "superBlock": "full-stack-developer",
+  "helpCategory": "JavaScript",
+  "challengeOrder": [{ "id": "687ad7be1ff45032ccf1d92f", "title": "Build a Theme Switcher" }],
+  "usesMultifileEditor": true
+}