Add XDP integration test

[Jake-Shadle]

This adds an XDP integration test that spins up a proxy using XDP in a separate network namespace, and a client + echo server that runs in another namespace. I attempted to get a k8s cluster working but fail miserably because k8s is too complicated, the network namespace solution is much easier.

[quilkin-bot]

Build Succeeded 🥳

Build Id: 0304bc7e-9070-43cc-a933-8dc1642ab89b

The following development images have been built, and will exist for the next 30 days:

• us-docker.pkg.dev/quilkin/ci/quilkin:0.10.0-dev-0dcd19e

To build this version:

git fetch [email protected]:googleforgames/quilkin.git pull/1078/head:pr_1078 && git checkout pr_1078
cargo build