Extract and set host header, return X-Powered-By

[ortz]

Summary

In order to use Veneur behind a webserver or a proxy, some changes need to be applied.
Veneur modifies the endpoint to avoid dns-caching and not preserving the original host header, this breaks Veneur if it sits behind a proxy that is listening to more than one site.

Motivation

Support usage of veneur behind another webserver / proxy (Nginx, Apache, etc...)
Adding visibility once it reached the veneur instance using X-Powered-By

Test plan

I wrote a test to verify the new extractHostPort works as expected and that I didn't break any other tests.

[ortz]

@ChimeraCoder fixed it to Veneur 1.2.0+ syntax

[cory-stripe]

Hey @ortz! To resay what @aditya-stripe already did, thanks for this!

We'll chat and decide if we're ready to go full 1.8, but this looks good otherwise. Thanks for the clear explanation and accompanying test.

[cory-stripe]

Update: We're working separately on moving fully to 1.8 which will pave the way for this.

[cory-stripe]

Hey @ortz! Mind rebasing this!

[cory-stripe]

Friendly ping! Mind rebasing @ortz?

[stripe-ci]

Gerald Rule: Copy Observability on Veneur and Unilog pull requests

cc @stripe/observability
cc @stripe/observability-stripe

[ortz]

@corey-stripe done

[corey-stripe]

Looks like this was meant for @cory-stripe :)

[ortz]

Hah :) yup.

[cory-stripe]

Sorry @ortz, master moved again. Give me another rebase and I'll get this in? (Sorry!)

[cory-stripe]

Hey @ortz can you rebase for me?

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