refactor(backend_log): use async readFile

using synchronous functions on the backend
is not recommended, as it is "blocking the event loop", i.e. no other tasks get executed/processed,
while the file is being read

src/routes/api/backend_log.ts

@@ -1,15 +1,15 @@
 "use strict";
 
-import fs from "fs";
+import { readFile  } from "fs/promises";
 import dateUtils from "../../services/date_utils.js";
 import dataDir from "../../services/data_dir.js";
 const { LOG_DIR } = dataDir;
 
-function getBackendLog() {
+async function getBackendLog() {
     const file = `${LOG_DIR}/trilium-${dateUtils.localNowDate()}.log`;
 
     try {
-        return fs.readFileSync(file, "utf8");
+        return await readFile(file, "utf8");
     } catch (e) {
         // most probably the log file does not exist yet - https://github.com/zadam/trilium/issues/1977
         return "";