(core) Add account page option to allow Google login

Summary:
Enabled by default, the new checkbox is only visible to
users logged in with email/password, and controls whether it is possible
to log in to the same account via a Google account
(with matching email). When disabled, CognitoClient will refuse logins
from Google if a Grist account with the same email exists.

Test Plan:
Server and browser tests for setting flag. Manual tests to verify
Cognito doesn't allow signing in with Google when flag is disabled.

Reviewers: paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D3257

app/gen-server/migration/1644363380225-UserOptions.ts

@@ -0,0 +1,17 @@
+import {nativeValues} from "app/gen-server/lib/values";
+import {MigrationInterface, QueryRunner, TableColumn} from "typeorm";
+
+export class UserOptions1644363380225 implements MigrationInterface {
+
+  public async up(queryRunner: QueryRunner): Promise<any> {
+    await queryRunner.addColumn("users", new TableColumn({
+      name: "options",
+      type: nativeValues.jsonType,
+      isNullable: true,
+    }));
+  }
+
+  public async down(queryRunner: QueryRunner): Promise<any> {
+    await queryRunner.dropColumn("users", "options");
+  }
+}