[TASK] Allow overriding the confirmation message finisher

Since #80187 it is possible to use the confirmation message finisher
within the form editor. This patch adds the missing possibility to
override the finisher within the content element.

Resolves: #85047
Related: #80187
Releases: master
Change-Id: I55e91972e1eb5ce0b636a8286423f4af2202ca03
Reviewed-on: https://review.typo3.org/57005


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>
Reviewed-by: Ralf Zimmermann <ralf.zimmermann@tritum.de>
Tested-by: Ralf Zimmermann <ralf.zimmermann@tritum.de>