chore: rename photo gallery (#44204)

* chore: rename files

* chore: update codebase

* chore: proper title case

Co-authored-by: Tom <20648924+moT01@users.noreply.github.com>

curriculum/challenges/_meta/learn-css-flexbox-by-building-a-photo-gallery/meta.json

@@ -1,7 +1,7 @@
 {
-  "name": "CSS Photo Gallery",
+  "name": "Learn CSS Flexbox by Building a Photo Gallery",
   "isUpcomingChange": true,
-  "dashedName": "css-photo-gallery",
+  "dashedName": "learn-css-flexbox-by-building-a-photo-gallery",
   "order": 20,
   "time": "5 hours",
   "template": "",