Well... No answer after 12 days, so I did the job :
https://github.com/Averell7/vingle-configure-smtp
BUT :
It is unfinished because :
1. The default value shown is "null", and it should be "smtp"
2. You can enter anything in the field and this is DANGEROUS. If you enter an invalid value, the forum will not load (blank page). It should be a drop down box with two possible values : mail or smtp.
Can anyone finish the job, or give me the indications to finish it. Thanks.
Changed files are :
extensions\vingle-configure-smtp\js\admin\dist\extension.js
extensions\vingle-configure-smtp\js\admin\src\components\ConfigureSMTPSettingModal.js