[BUG] [Java] Add Generated annotations to more classes

[jo1gi]

Fixes #17735

Adds Generated annotations to:

• RFC3339DateFormat
• ServerConfiguration
• ServerVariable
• ApiResponse
• ClassDiscriminatorMapping in JSON.mustache
• TypeReference in api.mustache

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Mentions: @bbdouglas @sreeshas @jfiala @lukoyanov @cbornet @jeff9finger @karismann @Zomzog @lwlee2608 @martin-mfg

[martin-mfg]

Thanks for the PR!
It mostly looks good to me. But what is the intention behind GenericTypeRef?

[jo1gi]

But what is the intention behind GenericTypeRef?

The inline TypeReference classes are also flagged if they don't have a Generated annotation. Creating a single TypeReference class (GenericTypeRef) was simpler than annotating all inline TypeReference classes.

[wing328]

@jo1gi looks like this break the build: https://github.com/OpenAPITools/openapi-generator/actions/runs/8612824195/job/23602824257

can you please take a look when you've time?

[wing328]

fixed in the latest master but there's another issue with JDK11 as the code now throws exception during runtime.

i've filed #18346 to revert back to TypeReference for the time being.