[REQ] [Java] API classes do not have a sufficient javadoc causing failing builds when running `mvn javadoc:javadoc` with `-Werror` enabled

Is your feature request related to a problem? Please describe.

When generating Java servers the API class defined in api.mustache and apiInterface.mustache does not have java doc.
When running mvn javadoc:javadoc this becomes a warning, which due to -Werror becomes an error and the build fails.

This is tested on openjdk version "17.0.9".

A PR is incoming.

Describe the solution you'd like

I propose additions to the api.mustache and apiInterface.mustache files so that there is some javadoc there.

For api.mustache (text borrowed from csharp/api.interface:

/**
 * Represents a collection of functions to interact with the API endpoints. 
 */

And the same for apiResponse.mustache:

/**
 * {{{notes}}}
 *
 {{#allParams}}
 * @param {{paramName}} {{description}}
 {{/allParams}}
 {{#responses}}
 * @return {{{message}}}
 {{/responses}}
 */

Describe alternatives you've considered

We've implemented two alternative solutions.

Exclusion in pom.xml

In our pom.xml we can exclude the files, but this is quite a big hammer because the files are very close to passing the checks.

Add a local api.mustache template with the needed changes

This solutions works a little better but requires us to copy the entire api.mustache and apiInterface.mustache files into our repository, making it much more cumbersome to migrate to a future version of openapi-generator.

Start with the Java server templates api.mustache, apiInterface.mustache, and apiResponse.mustache. Run mvn javadoc:javadoc with -Werror on a generated server to reproduce the warnings; done means the generated API classes have sufficient Javadoc and the build completes without Javadoc errors.