feat(backend-github): GitHub GraphQL API support (#2456)

* add GitHub GraphQL api initial support

* support mutiple backends for e2e tests - initial commit

* add github backend e2e test (currently skipped), fix bugs per tests

* refactor e2e tests, add fork workflow tests, support fork workflow in GraphQL api

* remove log message that might contain authentication token

* return empty error when commit is not found when using GraphQL (align with base class)

* disable github backend tests

* fix bugs introduced after rebase of GraphQL and OpenAuthoring features

* test: update tests per openAuthoring changes, split tests into multiple files

* fix: pass in headers for pagination requests, avoid async iterator as it requires a polyfill on old browsers

* test(e2e): disable github backend tests

packages/netlify-cms-backend-github/scripts/createFragmentTypes.js

@@ -0,0 +1,48 @@
+const fetch = require('node-fetch');
+const fs = require('fs');
+const path = require('path');
+
+const API_HOST = process.env.GITHUB_HOST || 'https://api.github.com';
+const API_TOKEN = process.env.GITHUB_API_TOKEN;
+
+if (!API_TOKEN) {
+  throw new Error('Missing environment variable GITHUB_API_TOKEN');
+}
+
+fetch(`${API_HOST}/graphql`, {
+  method: 'POST',
+  headers: { 'Content-Type': 'application/json', Authorization: `bearer ${API_TOKEN}` },
+  body: JSON.stringify({
+    variables: {},
+    query: `
+      {
+        __schema {
+          types {
+            kind
+            name
+            possibleTypes {
+              name
+            }
+          }
+        }
+      }
+    `,
+  }),
+})
+  .then(result => result.json())
+  .then(result => {
+    // here we're filtering out any type information unrelated to unions or interfaces
+    const filteredData = result.data.__schema.types.filter(type => type.possibleTypes !== null);
+    result.data.__schema.types = filteredData;
+    fs.writeFile(
+      path.join(__dirname, '..', 'src', 'fragmentTypes.js'),
+      `module.exports = ${JSON.stringify(result.data)}`,
+      err => {
+        if (err) {
+          console.error('Error writing fragmentTypes file', err);
+        } else {
+          console.log('Fragment types successfully extracted!');
+        }
+      },
+    );
+  });