added "backend log" dialog

src/routes/api/backend_log.js

@@ -0,0 +1,15 @@
+"use strict";
+
+const fs = require('fs');
+const dateUtils = require('../../services/date_utils');
+const {LOG_DIR} = require('../../services/data_dir.js');
+
+async function getBackendLog() {
+    const file = `${LOG_DIR}/trilium-${dateUtils.localNowDate()}.log`;
+
+    return fs.readFileSync(file, 'utf8');
+}
+
+module.exports = {
+    getBackendLog
+};