Follow internal redirects

[irl-segfault]

Please describe your use case / problem.
emissary-ingress/Ambassador does not currently expose a way to leverage Envoy's "Internal redirects" feature, whereby

Envoy supports handling 3xx redirects internally, that is capturing a configurable 3xx redirect response, synthesizing a new request, sending it to the upstream specified by the new route match, and returning the redirected response as the response to the original request.

The only redirects that emissary-ingress/Ambassador supports are statically defined redirects that are effectively hard-coded mappings.

Describe the solution you'd like
Expose configuration/Mapping knobs to leverage Envoy internal redirets.

Describe alternatives you've considered
No alternatives I can think of

Additional context
The example flow I'm thinking of is

Client sends a GET request for http://foo.com/bar
Upstream 1 sends a 302 with "location: http://baz.com/eep"
Envoy is configured to allow redirects on the original route, and sends a new GET request to Upstream 2, to fetch http://baz.com/eep with the additional request header "x-envoy-original-url: http://foo.com/bar"
Envoy proxies the response data for http://baz.com/eep to the client as the response to the original request.

[irl-segfault]

This is the same issue raised in #2846, which was sadly closed :(

[alexgervais]

Thanks for opening this feature request @irl-segfault! Is there a significant difference between your request and #2846, or would you be comfortable marking this one as a duplicate?

[irl-segfault]

fine marking this as duplicate

[alexgervais]

Closing in favor of this duplicate: #2846