feat(v2): generate sitemap (#1065)

* feat(v2): generate sitemap

* cannot snapshot sitemap because xml generated in different order

v2/lib/core/sitemap.js

@@ -0,0 +1,38 @@
+const sitemap = require('sitemap');
+
+module.exports = async function createSitemap({
+  siteConfig = {},
+  docsMetadatas = {},
+  pagesMetadatas = [],
+  blogMetadatas = [],
+}) {
+  const allMetadatas = [
+    ...blogMetadatas,
+    ...Object.values(docsMetadatas),
+    ...pagesMetadatas,
+  ];
+
+  const {url: siteUrl} = siteConfig;
+
+  if (!siteUrl) {
+    throw new Error('Url in siteConfig.js cannot be empty/undefined');
+  }
+
+  const urls = [];
+
+  allMetadatas.forEach(metadata => {
+    urls.push({
+      url: metadata.permalink,
+      changefreq: 'weekly',
+      priority: 0.5,
+    });
+  });
+
+  const sm = sitemap.createSitemap({
+    hostname: siteUrl,
+    cacheTime: 600 * 1000, // 600 sec - cache purge period
+    urls,
+  });
+
+  return sm.toString();
+};