Response interceptor

Can you please consider adding a feature to intercept the response HTML? Something like this:

```
function handler(event) {
var request = event.request;
var response = event.response;

// meta tags array
// Even better if we can fetch tags from DynamoDB in future?
const tags = [
{ name: “example1.domain.com”, value : “abc”},
{ name: “example2.domain.com”, value : “cuz”}
]

// find meta tags for custom domain
const meta = tags.find(x => x.name == request.host)

// Inject in index.html received from S3
response.content.replace(“<\head>”, ‘<\head>’

return response;
}
```