[TASK] Adding implementation class for finishers to the config, otherwise the preview breaks

Configuration/Yaml/Forms/FinisherSetupBE.yaml

@@ -5,6 +5,7 @@ TYPO3:
         standard:
           finishersDefinition:
             MailToSenderFinisher:
+              implementationClassName: SGalinski\SgMail\Finisher\Forms\FormsFinisher
               formEditor:
                 iconIdentifier: 't3-form-icon-finisher'
                 label: 'A Label that seems to be never used...'
@@ -19,6 +20,7 @@ TYPO3:
                     cc: ''
                     bcc: ''
             MailToReceiverFinisher:
+              implementationClassName: SGalinski\SgMail\Finisher\Forms\FormsFinisher
               formEditor:
                 iconIdentifier: 't3-form-icon-finisher'
                 label: 'A Label that seems to be never used...'