Insert a rate limit between requests as soon as the backend is back UP recently

[hamadodene]

Let's assume the case that we have a backend that has just restarted.

Once the backend starts up, it will presumably not be able to handle the load of requests that can come from the Carapace.

It would be interesting to be able to handle the case where the backend just went back UP. That is, as soon as the backend returns UP, for the first X seconds you should start with a low request load and gradually increase the request load.

This will probably mean that some requests will initially be pending, but still generally fewer requests should fail.