ISS-167739: Update Fern to support use default theme flag in documentation (#218)

* Update the latest default theme feature iOS documentations

* Move this code snippet and description in support section from UIKit

* Improve the documentation for dynamic theme configuration

* Make it sentence case for consistency

Author: dhananjayj-dev

fern/docs/pages/plug-sdk/ios/features.mdx

@@ -157,6 +157,14 @@ You can further customize the behavior by setting the `shouldDismissModalsOnOpen
 DevRev.shouldDismissModalsOnOpenLink: Bool
 ```
 
+## Dynamic theme configuration
+
+The DevRev SDK allows you to configure the theme dynamically based on the system appearance, or use the theme configured on the DevRev portal. By default, the theme will be dynamic and follow the system appearance.
+
+```swift
+DevRev.prefersSystemTheme: Bool
+```
+
 ## Session analytics
 
 The DevRev SDK offers session analytics features to help you understand how users interact with your app.