Add BaseGraphqlService, support [github] V4 API (#3763)

* add base class for Graphql APIs
* add GithubAuthV4Service + updates to GH token pool
* update github forks to use GithubAuthV4Service
* rename GithubAuthService to GithubAuthV3Service

core/base-service/json.js

@@ -0,0 +1,28 @@
+'use strict'
+
+// See available emoji at http://emoji.muan.co/
+const emojic = require('emojic')
+const { InvalidResponse } = require('./errors')
+const trace = require('./trace')
+
+function parseJson(buffer) {
+  const logTrace = (...args) => trace.logTrace('fetch', ...args)
+  let json
+  try {
+    json = JSON.parse(buffer)
+  } catch (err) {
+    logTrace(emojic.dart, 'Response JSON (unparseable)', buffer)
+    throw new InvalidResponse({
+      prettyMessage: 'unparseable json response',
+      underlyingError: err,
+    })
+  }
+  logTrace(emojic.dart, 'Response JSON (before validation)', json, {
+    deep: true,
+  })
+  return json
+}
+
+module.exports = {
+  parseJson,
+}