Added mirror support to avoid hitting remote constantly

scripts/fetch-artifact

@@ -0,0 +1,40 @@
+#!/bin/sh
+set -eu
+
+# Fetch helper contract:
+#   DEP_PKG_MIRROR=https://mirror.example.com/monok8s
+#   mirror URL = ${DEP_PKG_MIRROR}/${mirror_path}
+
+if [ "$#" -ne 3 ]; then
+    echo "usage: fetch-artifact <mirror-path> <output-file> <upstream-url>" >&2
+    exit 2
+fi
+
+mirror_path="$1"
+out="$2"
+upstream_url="$3"
+
+mkdir -p "$(dirname "$out")"
+rm -f "$out"
+
+if [ -n "${DEP_PKG_MIRROR:-}" ]; then
+    mirror_url="${DEP_PKG_MIRROR%/}/${mirror_path}"
+    echo "fetch-artifact: trying mirror: ${mirror_url}" >&2
+    if curl -fL --retry 3 -o "$out" "$mirror_url"; then
+        exit 0
+    fi
+    rm -f "$out"
+
+    if [ "${DEP_PKG_OFFLINE:-0}" = "1" ]; then
+        echo "fetch-artifact: mirror miss and DEP_PKG_OFFLINE=1: ${mirror_url}" >&2
+        exit 1
+    fi
+fi
+
+if [ "${DEP_PKG_OFFLINE:-0}" = "1" ]; then
+    echo "fetch-artifact: DEP_PKG_OFFLINE=1 and no usable mirror for ${mirror_path}" >&2
+    exit 1
+fi
+
+echo "fetch-artifact: fetching upstream: ${upstream_url}" >&2
+curl -fL --retry 3 -o "$out" "$upstream_url"