[Java][Client] Fix Deprecated annotation of deprecated operations

[michael-mutin]

There was:

• a PR: https://github.com/swagger-api/swagger-codegen/pull/6166
• and a Fix: https://github.com/swagger-api/swagger-codegen/pull/6801 . Those add the @Deprecated annotation to deprecated operations and the @deprecated javadoc annotation to their javadoc comments.

Then there was the migration that removed the isDeprecated property which lead to the annotations not being generated when needed. But the vendorExtension can be used instead, which I did.