Add support for OAuth authentication for Office365 or Gmail

@AdamPS: this is not always true, for example when company policies deny the usage of app passwords. Unfortunately issue https://github.com/symfony/symfony/issues/35528 has been closed with the comment "use app password" and issue https://github.com/symfony/symfony/issues/48888 is still opened. So I think this request is still relevant if after all this time on the symfony side nothing has been changed.

For people looking for a solution.

I found a gist online, untested, but it's a start.
https://gist.github.com/beerendlauwers/03acb112c80af0bf91546a05f790057a

@asplicios, thanks for your gist.

I have tried this gist and also try to change some how OAuthEsmtpTransportFactoryDecorator to be functional by adding

protected function getSupportedSchemes(): array
  {
    return ['office365'];
  }

but there is always an error that office365 scheme is not supported.
did you think about how schemes can be added.
Thanks