Summary:
Available at login.getgrist.com/signup, the new sign-up page
includes similar options available on the hosted Cognito sign-up
page, such as support for registering with Google. All previous
redirects to Cognito for sign-up should now redirect to the new
Grist sign-up page.
Login is still handled with the hosted Cognito login page, and there
is a link to go there from the new sign-up page.
Test Plan: Browser, project and server tests.
Reviewers: paulfitz
Reviewed By: paulfitz
Differential Revision: https://phab.getgrist.com/D3249
