Remove JSON.java from openapi ignore file.

[brendandburns]

cc @yue9944882

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[yue9944882]

telling from the comment, looks like we're stopping JSON generation due to the following two PRs:

• Fix issue #233 #240 might be a blocker as we have a test case asserting the html escape issue https://github.com/kubernetes-client/java/blob/master/kubernetes/src/test/java/io/kubernetes/client/openapi/JSONTest.java#L27
• Dropped reference to gson internal API #366 doesn't involve any functional changes, it was meant for better OSGi support

[yue9944882]

since we just bumped root version to 20.0.0-SNAPSHOT, we can try a code generation based on this PR to see if this is backward compatible. @brendandburns is there any other driver we want to refresh this JSON file generation?

[brendandburns]

@yue9944882 there were changes in the 6.x version of the generator which make this file (generated by 4,x) incompatible with the newly generated code. So this change is definitely necessary. We may have to backport these fixes too if we want to.

But yes, let's give it a try.

[yue9944882]

@brendandburns trying to pinpoint that incompatibility introduced. but it looks the last commit in the generator upstream was one year ago:

https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/resources/Java/libraries/okhttp-gson/JSON.mustache

so we're probably already using 6.x generator for a while, can you help me understand which part broke the compatibilty? 🤔

[brendandburns]

We've been previously locked on the 4.x release of the project, the PR to change that only merged in August:

https://github.com/kubernetes-client/gen/pull/247/files

That PR was done in an effort to migrate to jakarta.annotation instead of javax.annotation

[yue9944882]

@brendandburns gotcha, as a follow-up of this. i will cherry-pick the two PRs onto 6.x generated source code

[yue9944882]

/lgtm