feat(apps): package DATUM with stable service discovery

docker/datum/entrypoint.sh

@@ -0,0 +1,16 @@
+#!/bin/sh
+set -eu
+umask 077
+: "${BITCOIN_RPC_HOST:?Bitcoin host is required}"
+: "${BITCOIN_RPC_PASSWORD:?Bitcoin RPC password is required}"
+: "${DATUM_ADMIN_PASSWORD:?Datum admin password is required}"
+
+# Keep operator settings, including the payout address, across recreation.
+# Refresh platform-owned credentials and DNS names on every container start.
+config=/data/config.json
+if [ ! -e "$config" ]; then printf '{}\n' > "$config"; fi
+tmp=$(mktemp /data/config.json.XXXXXX)
+trap 'rm -f "$tmp"' EXIT HUP INT TERM
+jq -e -f /app/configure.jq "$config" > "$tmp"
+mv "$tmp" "$config"
+exec /app/datum_gateway --config "$config"