fix: add missing migrateConfig method, config versioning, and formatters module

ConfigManager.migrateConfig() was called but never defined — would crash at runtime.
Added config version checking, migration support, and fixed createEndpoint indentation.
New formatters module (csv, influxdb, json) for pluggable output formatting.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/helper/formatters/index.js

@@ -0,0 +1,58 @@
+/**
+ * Formatter Registry
+ * ------------------
+ * Maps format names to formatter modules.
+ * Each formatter exports: format(measurement, metadata) => string|object
+ *
+ * Usage:
+ *   const { getFormatter, registerFormatter } = require('./formatters');
+ *   const fmt = getFormatter('json');
+ *   const output = fmt.format('pump1', { fields: {...}, tags: {...} });
+ */
+
+const influxdbFormatter = require('./influxdbFormatter');
+const jsonFormatter = require('./jsonFormatter');
+const csvFormatter = require('./csvFormatter');
+
+// Built-in registry
+const registry = {
+  influxdb: influxdbFormatter,
+  json: jsonFormatter,
+  csv: csvFormatter,
+};
+
+/**
+ * Retrieve a formatter by name.
+ * @param {string} name - Format name (e.g. 'influxdb', 'json', 'csv')
+ * @returns {object} Formatter with a .format() method
+ * @throws {Error} If the format name is not registered
+ */
+function getFormatter(name) {
+  const formatter = registry[name];
+  if (!formatter) {
+    throw new Error(`Unknown output format: "${name}". Registered formats: ${Object.keys(registry).join(', ')}`);
+  }
+  return formatter;
+}
+
+/**
+ * Register a custom formatter at runtime.
+ * @param {string} name      - Format name
+ * @param {object} formatter - Object with a .format(measurement, metadata) method
+ */
+function registerFormatter(name, formatter) {
+  if (typeof formatter.format !== 'function') {
+    throw new Error('Formatter must have a .format(measurement, metadata) method');
+  }
+  registry[name] = formatter;
+}
+
+/**
+ * List all registered format names.
+ * @returns {string[]}
+ */
+function getRegisteredFormats() {
+  return Object.keys(registry);
+}
+
+module.exports = { getFormatter, registerFormatter, getRegisteredFormats };