[ccailly]

Checklist before requesting a review

• I have performed a self-review of my code.
• I have added tests (when available) that prove my fix is effective or that my feature works.
• I have updated the CHANGELOG with a short functional description of the fix or new feature.
• This change requires a documentation update.

Description

Add an "Email" form destination that sends a customized email when a form is submitted. It can be enabled from the plugin configuration page, under the new "Destinations" section.

• Subject and body reuse the core Title and Content fields: they accept form tags, and the body supports auto configuration.
• Recipients come from answers (email, requester, observer and assignee questions), specific users or groups, the form filler or their supervisor, and additional email addresses typed as tags (same dropdown as the actors fields of the ITIL objects).
• Inactive, deleted or expired users and groups with notifications turned off are skipped, as for GLPI notifications.
• Emails go through the notification queue, one per recipient. The body is sanitized, and a sending failure is logged without cancelling the submission.
• The config form, export, import and clone follow the native ITIL destinations.

Screenshots (if appropriate):