[TASK] Ext:form - Add update option to saveToDatabase finisher

This patch adds an option to the saveToDatabase finisher which makes it
possible to update an existing database record.
The forge issue provides an example extension for testing.

Resolves: #78839
Releases: master
Change-Id: I07d874a72b81a5e43c864f8a468a1310cac57995
Reviewed-on: https://review.typo3.org/50810


Reviewed-by: Bjoern Jacob <bjoern.jacob@tritum.de>
Tested-by: Bjoern Jacob <bjoern.jacob@tritum.de>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Daniel Lorenz <daniel.lorenz@extco.de>
Tested-by: Daniel Lorenz <daniel.lorenz@extco.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>