[Java] Default values for string-type header parameters are generated with two sets of quotes

Created by: sruehl

Description

Completely identical to #540 (closed) just that this time the problem exits for header values.

openapi-generator version

3.3.4

OpenAPI declaration file content or url

openapi: 3.0.0
info:
  title: Issue example
  version: 1.0.0
paths:
  /foo:
    get:
      parameters:
        - name: bar
          in: header
          required: false
          schema:
            type: string
            default: foobar
      responses:
        default:
          description: successful operation

Command line used for generation

java -jar openapi-generator-cli.jar generate -g spring -i openapi.yaml

Steps to reproduce

Related issues/PRs

#540 (closed)

Suggest a fix

#708 <- migrate mustach fixes from queryParams.mustache to headerParams.mustache