Add session metrics to XDP

[Jake-Shadle]

These metrics will be different than the ones in the session pool due to tracking sessions more coarsely, but should be good enough for testing purposes.

[XAMPPRocky]

Went through some other metrics and found some others missing.

Can we also add quilkin_packets_total, quilkin_bytes_total, and quilkin_packets_processing_duration? Either as a followup or in this?

[quilkin-bot]

Build Succeeded 🥳

Build Id: af7fa351-90a0-46be-a7bd-32294a6544b1

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-24e7ad6

To build this version:

git fetch [email protected]:googleforgames/quilkin.git pull/1105/head:pr_1105 && git checkout pr_1105
cargo build