Update AppSec Kit configuration documentation

[tamasmak]

Adds the vaadinPlatformVersion configuration option description to the AppSec Kit configuration documentation.

[github-actions]

AI Language Review

The file Advanced Topics has been updated with the following change:

1. A new configuration option, vaadinPlatformVersion, has been added to the AppSecConfiguration section. This option is described as the required Vaadin platform version that the application uses. It provides details on how the version is determined and the consequences if it is not specified.

There are no issues with clarity, accuracy, or completeness in the additions. The description is consistent with existing content and follows the established format. Furthermore, the text adheres to the guidelines for inclusive and understandable documentation. No further improvements are necessary based on the changes made.

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