Django 6.1 EMAIL_PROVIDERS support

[medmunds]

I'm helping with a proposed Django 6.1 feature that will probably impact django-mailer, and was hoping to get your input.

DEP-0018 will support multiple email backend configurations through a new EMAIL_PROVIDERS dict setting and mail.providers[alias] EmailBackend mapping (similar to caches, storages, and task_backends).

In particular, the recommended upgrades for wrapper EmailBackends are likely relevant.

If you have any feedback or concerns about the plans, we'd be very interested. Discussion is in django/deps#105 or Django Trac ticket-35514.

Thanks!