Deprecate vocadb-openapi-client-java in favour of vocadb-openapi-dto-java

[CXwudi]

Instead of generating the whole client, just generate the DTOs is better and allow users to use whatever client they want

However, it is shown that our hack of allowing Enum class name ended with "s" to support multiple unique enum value is necessary. Because in API call, such as GET /api/songs with the parameter fields, It must be a column separated list with unique elements like fields=tags,pvs. Using something else like fields=tags&fields=pvs won't work

We are also fixed in Jackson because the model is problematic with Gson, see https://github.com/CXwudi/vocadb-openapi-java-client-autofixer#before-generate

[CXwudi]

To generate the model only, we can reuse the command we have in https://github.com/VocaDB/vocadb-openapi-client-java but add --global-property models, see OpenAPITools/openapi-generator#12754 (comment)

However, not sure if it works for us

[CXwudi]

Actually, is it possible that Maven/Gradle excluding transitive dependencies would be enough?