[doc] [java/spring] x-YYY-extra-annotation doc is misleading

Description

the current java/spring doc reads:

List of custom annotations to be added to YYYY

So i was thinking: ok, i can write a yaml list if all my annotations that i want to add. eg.

      properties:
        foo:
          type: string
          x-field-extra-annotation:
            - "@MyCustomAnnotation1"
            - "@MyCustomAnnotation2"

WRONG

First one needs to understand that annotation in x-field-extra-annotation has nothing to do with java annotations even though the description suggests that IMO.

Second, there is no "List" here in a syntactical yaml/json sense, rather this extension may be used to add a list of java annotation there, but also a myriad of other things.

What this really does, is:

1. create a json-ish string from the value of x-field-extra-annotation (ie drop the quotes, replace : -> = )
2. put that as a text above the field

Hence, a more fitting name to the current behavior would be x-field-extra-text-above.

example:

        value:
          x-field-extra-annotation:
            foo:
              bar:
                 - 123
                 - ASDASD

will do this:

  {foo={bar=[123, ASDASD]}}
  private String value;

openapi-generator version

6.6.0

Locate the Java/Spring documentation for x-field-extra-annotation and compare its wording with the behavior and examples described in the issue. Update the explanation so it does not imply a YAML list of Java annotations and accurately describes the generated text; the documentation examples should reflect the shown output.