Allow to use custom authenticator by extending JWTAuthenticator

[fd6130]

Fix #915

This PR will allow user to use their own custom authenticator that is extends from JWTAuthenticator.

Currently allow one authenticator per firewall only.

namespace App\Security;

use Lexik\Bundle\JWTAuthenticationBundle\Security\Authenticator\JWTAuthenticator;

class CustomAuthenticator extends JWTAuthenticator
{
    // Your own logic
}

# config/services.yaml
services:
    app.custom_authenticator:
        class: App\Security\CustomAuthenticator
        parent: lexik_jwt_authentication.security.jwt_authenticator

# config/packages/security.yaml
security:
    # ...
    firewalls:
        # ...
        api:
            pattern:   ^/api
            stateless: true
            jwt: 
                authenticator: app.custom_authenticator

[chalasr]

Thank you @fd6130.