[make:security:custom] create a custom authenticator

[jrushlow]

Replaces the existing make:auth command that was originally used to implement authentication with "Guard" based authentication. When we created make:security:form-login - our aim was to ultimately remove make:auth.

• deprecates make:auth and it's MakeAuthenticator::class - deprecated in [make:auth] deprecate command #1523 for better changelog / release visibility
• introduces make:security:custom
• the "custom authenticator" generated replicates the example provided in the security docs: https://symfony.com/doc/current/security/custom_authenticator.html
• make:security:custom is intended to be no-frills... It will not work out of the box because it's a "custom" authenticator. The custom implementation details should be generated in userland.