Deprecation: #87200 - EmailFinisher "format" option
See forge#87200
Description
The 
        format option of the 
        \TYPO3\ has been marked as deprecated and
will be removed in TYPO3 11.0. It is replaced by the new 
        add option which can be used to disable HTML
and enforce plaintext-only mails. If set, mails will contain a plaintext and HTML part, otherwise only a plaintext part.
If the 
        format option is used, its value will be automatically migrated to 
        add:
format: htmlbecomesaddHtml Part: true format: plaintextbecomesaddHtml Part: false - a missing 
formatbecomesaddHtml Part: true  
Opening and saving a form with the form editor once also performs this migration and makes it permanent.
Impact
The 
        format option will no longer work in TYPO3 11.0.
Affected Installations
All installations which use EXT:form and its 
        \TYPO3\.
Migration
Replace 
        format: html with 
        add.
Replace 
        format: plaintext with 
        add.