[misc] bump metrics module to 3.4.1

- renamed package from `metrics-sharelatex` to `@overleaf/metrics`
- drop support for statsd backend
- decaffeinate
- compress `/metrics` response using gzip
- bump debugging agents to latest versions
- expose prometheus interfaces for custom metrics (custom tags)
- cleanup of open sockets metrics
- fix deprecation warnings for header access

services/notifications/app/js/Notifications.js

@@ -14,7 +14,7 @@
 let Notifications
 const logger = require('logger-sharelatex')
 const { db, ObjectId } = require('./mongodb')
-const metrics = require('metrics-sharelatex')
+const metrics = require('@overleaf/metrics')
 
 module.exports = Notifications = {
   getUserNotifications(user_id, callback) {

services/notifications/app/js/NotificationsController.js

@@ -12,7 +12,7 @@
  */
 const Notifications = require('./Notifications')
 const logger = require('logger-sharelatex')
-const metrics = require('metrics-sharelatex')
+const metrics = require('@overleaf/metrics')
 
 module.exports = {
   getUserNotifications(req, res) {