Small enhancement - additional option to specify headers

[japzio]

Added requestHeaders map to be able to specify additional headers. Can be used if apidocs url is protected by basicAuth or setting custom url to generated openapi spec json|yaml

     requestHeaders = [
       "x-forwarded-host": "custom-host",
       "x-forwarded-port": "7000"
    ]

Ref feature https://github.com/springdoc/springdoc-openapi-maven-plugin