add some error handling around common issues (#16387)

Author: sarahs

script/graphql/update-files.js

@@ -15,6 +15,20 @@ const processUpcomingChanges = require('./utils/process-upcoming-changes')
 const processSchemas = require('./utils/process-schemas')
 const prerenderObjects = require('./utils/prerender-objects')
 
+// check for required PAT
+if (!process.env.GITHUB_TOKEN) {
+  console.error('Error! You must have a GITHUB_TOKEN set in an .env file to run this script.')
+  process.exit(1)
+}
+
+// check for required Ruby gems (see note below about why this is needed)
+try {
+  execSync('gem which graphql')
+} catch (err) {
+  console.error('\nYou need to run: bundle install')
+  process.exit(1)
+}
+
 // TODO this step is only required as long as we support GHE versions *OLDER THAN* 2.21
 // as soon as 2.20 is deprecated on 2021-02-11, we can remove all graphql-ruby filtering
 const removeHiddenMembersScript = path.join(__dirname, './utils/remove-hidden-schema-members.rb')