Allow for up to 2 CloudFront functions to be associated - Added WAF support

[bendubuisson]

You can now associate both available CF functions (viewer-request and viewer-response):

  cloudfront_function_association = [
    {
      event_type   = "viewer-request"
      function_arn = aws_cloudfront_function.viewer-request-function.arn
    },
    {
      event_type   = "viewer-response"
      function_arn = aws_cloudfront_function.viewer-response-function.arn
    },
  ]