feat: Add a documentation layout design for public help center portal (#14403)

https://github.com/user-attachments/assets/fc4d15f9-2b54-4627-940f-94772ec739b1

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Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>
Co-authored-by: Sivin Varghese <64252451+iamsivin@users.noreply.github.com>

theme/colors.js

@@ -227,6 +227,9 @@ export const colors = {
 
     black: '#000000',
     brand: '#2781F6',
+    portal: 'var(--dynamic-portal-color)',
+    'portal-soft': 'var(--dynamic-portal-color-soft)',
+    'portal-faint': 'var(--dynamic-portal-color-faint)',
     background: 'rgb(var(--background-color) / <alpha-value>)',
     'input-background': 'rgba(var(--background-input-box))',
     surface: {