tonic: Introduce a new method on Endpoint to override the origin

[QuentinPerez]

Motivation

At @znly, we use Envoy as a service mesh to distribute the traffic across the services.
Meaning that:

• we have an auto-scaled farm of Envoy which proxy the entire traffic.
• we have to refresh the IPs periodically (due to auto-scaling).
• we have to talk to the IPs directly.

That said, the requests end with an unavailable error, why? because Envoy is called with the URI (the IP in our case) and can't determine which service we are trying to reach.

Solution

A new method named origin has been added to override the origin sent.
We tried it in production and it's working fine.
Let me know if you have a better solution.

[QuentinPerez]

@LucioFranco 👋🏻
Let me know if you need more explanation or time to review this PR

[LucioFranco]

LGTM only thing missing I think is a simple unit test.

[LucioFranco]

Thanks!

[QuentinPerez]

@LucioFranco thx ! do you think that we could have a minor soon ? do not want to stay on my fork too long :)

[LucioFranco]

I think we can get a release out pretty soon here, I just need to consider if we want to make a prost release as well which might delay tonic's. So hopefully this week if not next week.