Is your feature request related to a problem? Please describe.
The events.LambdaFunctionURLResponse doesn't support MultiValueHeaders which became in come use. For now, the workaround is to set up the APIGatewayv2 instance and use events.APIGatewayV2HTTPResponse, which sometimes doesn't provide an economic reason to use APIGatewayv2 just for small Lambda.

Describe the solution you'd like
I would like to ask you to implement MultiValueHeaders support for events.LambdaFunctionURLResponse, bellow you can check the structure example:

type LambdaFunctionURLResponse struct {
    StatusCode        int                 `json:"statusCode"`
    Headers           map[string]string   `json:"headers"`
    MultiValueHeaders map[string][]string `json:"multiValueHeaders"`
    Body              string              `json:"body"`
    IsBase64Encoded   bool                `json:"isBase64Encoded"`
    Cookies           []string            `json:"cookies"`
}

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.