Verify SAML config should display required assertions when Group Managed Accounts is enabled

What

In #33464 (closed) we introduced a way to view parts of the SAML XML to help users verify that the configuration is correct.

When group managed accounts is enabled we should show an error if Email is not present in the assertions, and should show how the name will be created.

Why

This will help avoid hitting problems when users try to sign up to GitLab.com, and will help group admins track down the cause of the problem