Keep linebreaks in the contract in generated Java code

Description

Line-breaks in yaml contracts currently get lost in the javadoc comment (they are replaced by a blank).
To keep line-breaks also in dynamically generated contracts, they should be replaced by \n.

Swagger-codegen version

2.2.2

Swagger declaration file content or url

Example (adapted 2.0\petstore.yaml)

paths:
  /pet:
    post:
      tags:
        - pet
      summary: 'Add a new pet to the store
      test second line'

output:

    @io.swagger.annotations.ApiOperation(value = "Add a new pet to the store test second line", notes = "", response = Void.class, authorizations = {
...

Suggest a Fix

1. Keep line breaks by generating \n instead of " " for line breaks
2. To also keep line breaks in dynamically generated contracts, an escaped line break needs to be added ("\n").

Reproduce the issue with the YAML contract example and inspect the Java generation path that produces the ApiOperation Javadoc values. Confirm that embedded line breaks are represented as escaped \n in the generated Java output, and add coverage if the relevant generation test area is found.