Documentation improvement: How to use Microsoft OAuth with PHPMailer

[Synchro]

Now that Microsoft have discontinued their support for simple username/password authentication, many people are trying to switch to use XOAUTH2 instead. Unfortunately this appears to be a complete nightmare, as discussed in #2747, #2116, #1959, #1901, etc. A wiki article detailing how to set it up would be much appreciated by many of PHPMailer's users.

[greew]

I'll probably add a wiki page with a detailed explanation tomorrow 😊

[greew]

Here we go!

https://github.com/PHPMailer/PHPMailer/wiki/Microsoft-Azure-and-XOAUTH2-setup-guide

I'll have a Pull Request in a few minutes with additions for get_oauth_token.php and an azure example file :)

[Synchro]

Thanks for all your effort on this. Hopefully Microsoft will make it easier and more reliable at some point, but until then...