Fixed small issue where explicitly defined response header would be overwritten when using the reverse proxy functionality

[dukeofharen]

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

Fixed small issue where explicitly defined response header would be overwritten when using the reverse proxy functionality.

What is the new behavior?

When you specifically define a response header, the response header will always overwrite the value that is set by the reverse proxy response writer.

- id: proxy-test-1
  conditions:
    method: GET
    url:
      path:
        startswith: /todoitems
  response:
    headers:
      X-Header: value-from-stub
    reverseProxy:
      url: https://jsonplaceholder.typicode.com
      appendPath: true
      appendQueryString: true
      replaceRootUrl: true

Does this introduce a breaking change?

• Yes
• No