split feign client generator

[mshima]

Split feign-client generator to reduce unused files.

• feign client is not used by default, looks an leftover of old microservice support.
• OAuthIdpTokenResponseDTO is currently generated for every oauth2 app, but only used by feign. Move to feign-client and cleanup.
• add migration for new option, enable feignClient for old applications, disabled for new applications.
• add option/prompt/jdl support.

Fixes #20102

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