Add Kotlin examples for Spring Data Integration of servlet application

[talerngpong]

Expected Behavior

It should provide both of Java and Kotlin examples for Spring Data Integration with servlet application.

Current Behavior

It provides only Java examples.

Context

When walking through Servlet API integration, its page contains both of Java and Kotlin examples for the integration by toggling. Then, after walking to its next page of Spring Data Integration, there are only Java examples.

[marcusdacoregio]

Thanks for submitting this @talerngpong.

Are you interested to submit a PR that adds the examples?

[talerngpong]

@marcusdacoregio Yes. Here is my PR (#10834).

[marcusdacoregio]

I will change this to be a bug because we want to backport the fix to older versions.

[marcusdacoregio]

Closed via #10834