[TASK] Finishing sg mail forms integration & standard contact form

Classes/Finisher/Forms/FormsFinisher.php

Classes/Service/FormhandlerFinisherService.php

Configuration/MailTemplates/Template1.php

Configuration/MailTemplates/Template2.php

Configuration/TypoScript/setup.ts

Configuration/Yaml/Forms/BaseSetup.yaml

Configuration/Yaml/Forms/CustomFormSetup.yaml

Configuration/Yaml/Forms/FormEditorSetup.yaml

Resources/Private/Forms/Partials/Field/Field.html

Resources/Private/Forms/Partials/Textarea.html

Resources/Private/Forms/contactForm.yaml

Resources/Private/Language/de.locallang.xlf

Resources/Private/Language/locallang.xlf

Resources/Private/Templates/SgMail/Template1/template.html

Resources/Private/Templates/SgMail/Template2/template.html