namecheap: slow down requests for rate limit

https://www.namecheap.com/support/knowledgebase/article.aspx/9739/63/api-faq/#z

src/dns/namecheap.js

@@ -19,6 +19,7 @@ const assert = require('assert'),
     network = require('../network.js'),
     safe = require('safetydance'),
     superagent = require('superagent'),
+    timers = require('timers/promises'),
     util = require('util'),
     waitForDns = require('./waitfordns.js'),
     xml2js = require('xml2js');
@@ -39,6 +40,9 @@ async function getQuery(domainConfig) {
 
     const ip = await network.getIPv4(); // only supports ipv4
 
+    // https://www.namecheap.com/support/knowledgebase/article.aspx/9739/63/api-faq/#z . 50 / minute
+    await timers.setTimeout(5000); // limits to 12req/min for this process. we can have 3 apptasks in parallel
+
     return {
         ApiUser: domainConfig.username,
         ApiKey: domainConfig.token,