[Java][Feign] fix param-annotation handling ( issue-6069 )

Created by: Chr1st0ph

This is a fix for https://github.com/OpenAPITools/openapi-generator/issues/6069

My first try to solve this issue (https://github.com/OpenAPITools/openapi-generator/issues/5249) failed pitiful because of different reasons. In order to verify the results of this change ( also for future changes ) I added a first test-case for Feign-client-code-generation.

This test-case is quite complex.

Possible alternatives ( imho ):

• Integration-test using a generated Feign-client instance for talking to a mock-server
• simple string-comparison of generated code

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