Set up Cognito authN for the visits page

[arlindohall]

We want to require a makerspace employee to set up the visits page one time before it can be used by visitors. This means we need to add a Cognito authorizer to the page that only allows pre-cleared Makerspace employees to sign up, and requires them to sign in before it shows the actual visitors page. This authorizer should check whether the user is allow-listed before letting them sign up.

If possible, this should also integrate with the page in a way that lets the page stay signed in and functional even on a hard refresh via a cookie.

I don't actually know whether Cognito has this functionality built-in or if we'll need to bake something ourselves.