Support for OAuth authentication in django.core.mail.backends.smtp.EmailBackend

### Code of Conduct

- [x] I agree to follow Django's Code of Conduct

### Feature Description

Support for the apparently more modern authentication method SASL (X)OAuth 2.0 in django.core.mail.backends.smtp.EmailBackend (or a new SMTP backend with this newer way of authenticating)

### Problem

A lot of providers seems to be turning off support for sending mails using SMTP, in particular with the original authentication method.
from https://github.com/simonrob/email-oauth2-proxy#example-use-cases:
* You need to use an Office 365 email account, but don't get on with Outlook. The email client you like doesn't support OAuth 2.0, which became mandatory for IMAP/POP [in January 2023](https://techcommunity.microsoft.com/t5/exchange-team-blog/basic-authentication-deprecation-in-exchange-online-september/ba-p/3609437) ([September 2024 for personal Hotmail/Outlook accounts](https://support.microsoft.com/en-us/office/modern-authentication-methods-now-needed-to-continue-syncing-outlook-email-in-non-microsoft-email-apps-c5d65390-9676-4763-b41f-d7986499a90d); [late 2027 for O365 SMTP](https://techcommunity.microsoft.com/t5/exchange-team-blog/exchange-online-to-retire-basic-auth-for-client-submission-smtp/ba-p/4114750)).
* You used to use Gmail via IMAP/POP/SMTP with your raw account credentials (i.e., your real password), but cannot do this now that Google has disabled this method, and don't want to use an [App Password](https://support.google.com/accounts/answer/185833) (or cannot enable this option).

### Request or proposal

request

### Additional Details

Implementation specific alternatives could be used per mail provider (e.g like https://pypi.org/project/django-msgraphbackend/ for MS Exchange), but I could not find any "de jure" alternatives for this with comfortably high amount of users.

[Postfix sasl-xoauth2 plugin](https://github.com/tarickb/sasl-xoauth2) has some info regarding what/how

### Implementation Suggestions

_No response_

Start with django.core.mail.backends.smtp.EmailBackend and review how its current authentication flow is structured. Compare the requested SASL XOAuth2 support with the provider-specific alternatives mentioned, then define the supported scope and how completion would be tested for SMTP providers.

Written by the indexing model from the issue text.