fix(deploy): align vector bootstrap identity policy

scripts/vector-rotate-bootstrap-password.sh

@@ -2,6 +2,7 @@
 set -eu
 
 cd "$(dirname "$0")/.."
+. ./deploy/vector/secret-policy.sh
 
 if [ "$#" -ne 2 ]; then
   echo "usage: $0 OLD_SECRET_FILE NEW_SECRET_FILE" >&2
@@ -15,12 +16,8 @@ absolute_file() {
 
 old_secret=$(absolute_file "$1")
 new_secret=$(absolute_file "$2")
-for secret in "$old_secret" "$new_secret"; do
-  if [ ! -f "$secret" ] || [ ! -r "$secret" ] || [ ! -s "$secret" ]; then
-    echo "secret file must be a readable, non-empty regular file: $secret" >&2
-    exit 2
-  fi
-done
+validate_secret_file "$old_secret" old_bootstrap_secret
+validate_secret_file "$new_secret" new_bootstrap_secret
 if [ "$old_secret" -ef "$new_secret" ]; then
   echo "old and new secret files must be distinct" >&2
   exit 2