[DOCS] Update finisher documentation

The whole documentation about finishers has not
been touched since ages. A lot of information are
outdated. This patch fixes the mess.

Also improve a language label to clarify the usage of
the title field within the finishers "EmailToReceiver"
and "EmailToSender".

Resolves: #96048
Releases: main, 11.5
Change-Id: I3004194c37203993582e7f4687523ad766d3235d
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/74474


Tested-by: core-ci <typo3@b13.com>
Tested-by: Mathias Brodala <mbrodala@pagemachine.de>
Tested-by: waldhacker <hello@waldhacker.dev>
Reviewed-by: Mathias Brodala <mbrodala@pagemachine.de>
Reviewed-by: waldhacker <hello@waldhacker.dev>