chore(starters): add gatsby-starter-casual (#17529)

added gatsby-starter-casual design by startbootstrap

Author: jodharishi

docs/starters.yml

@@ -3869,3 +3869,16 @@
     - New Header
     - Responsive
     - Sidebar that displays recent blog posts
+- url: https://anubhavsrivastava.github.io/gatsby-starter-casual
+  repo: https://github.com/anubhavsrivastava/gatsby-starter-casual
+  description: Multi page starter based on the Casual site template by startbootstrap for portfolio
+  tags:
+    - Onepage
+    - Styling:SCSS
+    - PWA
+  features:
+    - Designed by startbootstrap
+    - Fully Responsive
+    - Styling with SCSS
+    - Offline support
+    - Web App Manifest