Container entrypoints were rendered as `fmt.Sprintf` shell strings in Go, so
every entrypoint fix needed a full operator release, nothing was shellcheckable,
and the escaping was a hazard.
How:
- Add a `kea-init` initContainer that finalises the per-pod config and
bounded-waits for HA peer DNS, replacing the in-entrypoint retry. It hardens
the shared run dir to 0750, substitutes `this-server-name` from the pod
ordinal (`POD_NAME` via the downward API), stages both configs into the shared
emptyDir, and gates on `kea-dhcp4 -t` (60x2s) — failing loud after the cap so
the kubelet restarts it instead of starting a doomed server.
- Run the main kea-dhcp4 / kea-ctrl-agent containers with kea exec'd directly,
dropping both wrapper shells.
- Replace the two `fmt.Sprintf` entrypoints with a single committed
`internal/kea/scripts/init.sh` embedded via `go:embed` and parameterised
entirely by env vars — no Go string interpolation.
- Add a shellcheck step to the pre-commit pipeline.
Test:
- Assert the pod shape: one kea-init initContainer, POD_NAME from the downward
API, main containers exec kea directly, and the ConfigMap carries init.sh (not
the old per-container entrypoints).
- Assert init.sh hardens the socket dir, gates on `kea-dhcp4 -t`, fails loud
after the cap, and is free of fmt verbs.
- shellcheck the embedded script.
