Fix Privacy Settings Password Required Template & Wire In Florence SSO To Privacy Settings

[sanjeevz3009]

What is the context of this PR?

This PR is a initative taken after reviewing #568 where I uncovered the below issues, which this PR aims to address.

This PR addresses several issues:

• First one being, currently when a user sets a page behind a password protection using the page privacy setting -> when the user visits the live URL -> 404. -> when it's meant to show the password_required.html template. We have missed this during the NonTrailingSlashRedirectMiddleware work.
• I have also improved the UI/ UX for the password_required.html template and how it surfaces the error to the user etc.
  • This has been fixed on this PR, and the front-end template has been improved.
• The second enhancement is around when we use the privacy settings to have a page behind Private, accessible to any logged-in users or Private, accessible to users in specific groups options, then we render the login_page.html template, and the logic behind it would not work due to WAGTAIL_CORE_ADMIN_LOGIN_ENABLED=False/ Wagtail core login being turned off in the deployed environments. + This template UI design/ UX needs improving.
  • I have fixed the core issue where, when users use the options to have a page behind a login wall, such as a user must be logged in or logged in and be part of a certain group -> then it will redirect the user to the Florence SSO page, and the user can be authenticated using that.

How to review

• Read the following doc: https://docs.wagtail.org/en/stable/advanced_topics/privacy.html
• Make sure the above issues are resolved:
  • No 404 when visiting a page that's password-protected
  • When Congito is enabled, you can successfully log in and view a page behind Private, accessible to any logged-in users or Private, accessible to users in specific groups page privacy options. To do this, you will need to use the dis-authentication-stub locally to try to simulate the SSO user journey/ flow. See the PR description on how: feat(auth): add AWS Cognito JWT authentication support #163
• Play around with the password_required.html template form features and make sure the errors are surfaced properly now to the user.

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Follow-up Actions

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