Refresh Cognito reference page

[kenjenkins]

It looks like the Cognito screenshots were last updated around a year and a half ago. I think the AWS console interface for Cognito has changed a bit since then.

Let's consider updating the screenshots and instructions to match the current UI.

For example, it looks like some of the app client settings have been renamed:

• 'OAuth 2.0 grant types' instead of 'Allowed OAuth Flows'
• 'OpenID Connect scopes' instead of 'Allowed OAuth Scopes')

Originally posted by @kenjenkins in #1138 (comment)