[kotlin-spring] add support for the delegate pattern

Created by: massimosiani

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Description of the PR

(details of the change, additional tests that have been done, reference to the issue for tracking, etc)

Fixes #2526 (closed) by introducing the delegatePattern option. The resulting output is the kotlin version of the Java code. Please notice that the reactive option is not supported yet, as I'm not confident with coroutines.

No drawback compatibility issue should arise.

cc @dr4ke616.