The go-metrics-graphite package has been unmaintained for 10+ years,
which is a packaging and supply-chain concern for downstream
distributors (see #1831). Nebula only used its Config struct and Once()
entrypoint, so inline just those (~65 lines) into a local graphite.go,
preserving the upstream BSD-2-Clause copyright notice, and remove the
dependency.
Fixes#1831
Co-authored-by: Claude <svc-devxp-claude@slack-corp.com>
