Reimplement CPE debug log

lib/config.ts

@@ -80,6 +80,8 @@ const options = {
   DOWNLOAD_TIMEOUT: { type: "int", default: 3600 },
   EXT_TIMEOUT: { type: "int", default: 3000 },
   MAX_CACHE_TTL: { type: "int", default: 86400 },
+  DEBUG_FILE: { type: "path", default: "" },
+  DEBUG_FORMAT: { type: "string", default: "yaml" },
   DEBUG: { type: "bool", default: false },
   RETRY_DELAY: { type: "int", default: 300 },
   SESSION_TIMEOUT: { type: "int", default: 30 },