modules/monitoring: migrate monitoring vpn secrets to age

bin/add-secret.sh

@@ -0,0 +1,15 @@
+#!/bin/bash
+
+set -euo pipefail
+
+cd $(git rev-parse --show-toplevel)
+
+host=$1
+secret=$2
+
+mkdir -p hosts/${host}/secrets
+
+nix run github:ryantm/agenix -- -e hosts/${host}/secrets/new
+
+mv hosts/${host}/secrets/new hosts/${host}/secrets/${secret}.age
+