Add terms disclaimer to Group SAML sign in page

What does this MR do and why?

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Follow-up to !99193 (merged) which was a fix related to https://gitlab.com/gitlab-org/gitlab/-/issues/339256.

The global GitLab sign-in/registration page shows the disclaimer By clicking Register or registering through a third party you accept the GitLab Terms of Use and acknowledge the Privacy Policy and Cookie Policy. However, the Group SAML sign-up page did not, although the recent changes to registration flow also affected Group SAML. This change adds the disclaimer to the Group SAML sign-in page, too.

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