Enable the use of `AllowUnverifiedEmailSignIns` for Email provider

Background: (The comment, as well as the original issue) For the Email auth provider, Supabase lets users configure whether the user "will need to confirm their email address before signing in for the first time". This field configures the Autoconfirm field in the mailer configuration used by the auth backend, and depending on this field: • If set to true, the new user's email address is considered auto-verified. • If set to false, new user registrations are required to confirm their email before they can sign in. - this limits the ability to offer a user experience where users can still sign into their accounts without verified emails, but with limited functional capabilities. I believe the MailerConfiguration.AllowUnverifiedEmailSignIns field, which defaults to "false" for the Email auth provider, is well-suited to address this limitation. Currently, I see this field used only for external auth providers. However, I think its use …