Fix duplicate Prebid sidebar translation key

Added unique 'key' attributes to both Prebid categories to resolve duplicate translation key conflict in Japanese locale:
- Prebid category under Web: key 'Prebid-Web'
- Prebid category at Mobile level: key 'Prebid-Mobile'

This fixes the build error: 'Multiple docs sidebar items produce the same translation key'

Author: sunnywu

sidebars.js

@@ -120,6 +120,7 @@ const fullSidebar = [
                 {
                   type: 'category',
                   label: 'Prebid',
+                  key: 'Prebid-Web',
                   link: {
                     type: 'doc',
                     id: 'guides/integration-prebid',
@@ -169,6 +170,7 @@ const fullSidebar = [
           {
             type: 'category',
             label: 'Prebid',
+            key: 'Prebid-Mobile',
             link: {
               type: 'doc',
               id: 'guides/integration-prebid',