Configuration overhaul: make mail-related configuration clearer

[josecelano]

Refactor configuration for options related to email in the registration.

Old version

[auth]
email_on_signup = "optional"

[mail]
email_verification_enabled = false

New version

Registration Disabled:

# [registration]

Registration without email option:

[registration]

Registration optionally including an email address:

[registration]
[registration.email]

Registration with email:

[registration]
[registration.email]
required = true

Registration with optional email, but if email is supplied it is verified:

[registration]
[registration.email]
verified = true

Registration with email and email is verified:

[registration]

[registration.email]
required = true
verified = true

Subtasks

• Add the new section
• Use new values in the code
• Delete old config option

[josecelano]

Hi @da2ce7 I think I would change this:

[registration]

  [registration.email] 
  required = true
  verified = true

To this:

[registration]

  [registration.email]
  required = true
  verification_required = true

I think it's less ambiguous, for example, in this real piece of code:

// Fail login if email verification is required and this email is not verified
if let Some(registration) = &settings.registration {
    if let Some(email) = &registration.email {
        if email.verified && !user_profile.email_verified {
            return Err(ServiceError::EmailNotVerified);
        }
    }
}

With the new name would be:

// Fail login if email verification is required and this email is not verified
if let Some(registration) = &settings.registration {
    if let Some(email) = &registration.email {
        if email.verification_required && !user_profile.email_verified {
            return Err(ServiceError::EmailNotVerified);
        }
    }
}

[josecelano]

ACK 8d660b8