chore: Migrate authentication to new tables (#1929)

This work provides a foundation for a more pluggable authentication system such as the one outlined in #1317.

closes #1317

server/utils/startup.js

@@ -0,0 +1,21 @@
+// @flow
+import { Team, AuthenticationProvider } from "../models";
+
+export async function checkMigrations() {
+  if (process.env.DEPLOYMENT === "hosted") {
+    return;
+  }
+
+  const teams = await Team.count();
+  const providers = await AuthenticationProvider.count();
+
+  if (teams && !providers) {
+    console.error(`
+This version of Outline cannot start until a data migration is complete.
+Backup your database, run the database migrations and the following script:
+
+$ node ./build/server/scripts/20210226232041-migrate-authentication.js
+`);
+    process.exit(1);
+  }
+}