[enhancement] [jaxrs-spec] Add builders to models

Created by: shybovycha

Note: this is a resurrection of #4916, since that branch has been rebased on top of master and CIs did not quite like me changing the target branch

As per #2415, adding builders generation for models.

The reasons for this change are:

1. currently, the setters do not have the set prefix, which makes models not comply with java beans requirements
2. constructing models becomes painful, specifically when they have numerous fields

Compare the current way to construct a model to the proposed one:

now:

new Model().property1(value1).property2(value2)

// getters/setters

myModel.getProperty1();
myModel.property1(value1);

proposed:

Model.builder().property1(value1).property2(value2).build()

// getters/setters

myModel.getProperty1();
myModel.setProperty1(value1);

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