[FEATURE] Integrate Swift Mailer's spool transport

Adds new configuration to the install tool and provides an
extbase schedular task and command.

A small refactoring was required:
* Moved transport creation from mailer to a factory

Possible issues are:
* sending of memory-spooled messages is a bit hacky

Resolves: #76349
Releases: master
Change-Id: I9736d4f943eea2052bf935ac1fc055c336894397
Reviewed-on: https://review.typo3.org/49182


Reviewed-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Tested-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>