[Mime] Simplify adding Parts to an Email

[fabpot]

Q	A
Feature PR	symfony/symfony#47462
PR author(s)	@fabpot
Merged in	6.2

[wouterj]

This should be documented together with #17353

The sections that require update (using addPath() instead of attach*()/embed*()) are https://symfony.com/doc/current/mailer.html#file-attachments and https://symfony.com/doc/current/mailer.html#embedding-images I think.

[hiddewie]

I made #17372 to document both symfony PRs.