Instrument warm-server via Datadog (#16566)

Co-author: @chiedo

Co-authored-by: Chiedo John <2156688+chiedo@users.noreply.github.com>

Author: JasonEtco

lib/warm-server.js

@@ -1,7 +1,8 @@
+const statsd = require('./statsd')
 const fetchEarlyAccessPaths = require('./fetch-early-access-paths')
 let pages, site, redirects, siteTree, earlyAccessPaths
 
-module.exports = async function warmServer () {
+async function warmServer () {
   if (!pages) {
     if (process.env.NODE_ENV !== 'test') {
       console.log('Priming context information')
@@ -22,3 +23,7 @@ module.exports = async function warmServer () {
     pages, site, redirects, siteTree, earlyAccessPaths
   }
 }
+
+// Instrument the `warmServer` function so that
+// it's wrapped in a timer that reports to Datadog
+module.exports = statsd.asyncTimer(warmServer, 'warm_server')