Built-in support for something similar to nginx proxy_redirect default

Tried to read everything in both https://github.com/microsoft/reverse-proxy/issues/21 and https://github.com/microsoft/reverse-proxy/issues/13, plus related PRs, and did tests myself.

But I can't find anything like a built-in feature similar to that of nginx' `proxy_redirect default` (which is enabled there by default).

So, before I start implementing my own (using response transforms), just want to make sure I didn't miss anything? And, of course, also, if it's not there, I'd suggest it as a great improvement. 😃

Gist of what I'm looking for:

```c#
.AddTransforms(transformBuilderContext =>
{
transformBuilderContext.AddResponseTransform(async transformContext =>
{
await transformContext.RedirectProxyLocationOfNewResource();
});
})
```

where `RedirectProxyLocationOfNewResource` would implement something like

```
// => POST http://service.myproxy.com {...}
// => POST https://some-backend-service.com {...}
// <= HTTP 201: Location: https://some-backend-service.com/path/to/resource
// <= HTTP 201: Location: http://service.myproxy/path/to/resource
```