Improve pasting email content into ticket follow-ups

[jmd-92160]

Helpdesk agents frequently need to copy part of an email conversation into a ticket follow-up.

The current workflow is to manually select only the relevant part of the email (usually from the From: header to the signature) and paste it into GLPI.
This approach is preferred because it allows the user to keep only the relevant message instead of the entire email thread.

However, the pasted content is not preserved consistently.

Expected behavior:
When content copied from an email client (such as Microsoft Outlook classic version) is pasted into a follow-up, GLPI should preserve as much of the original content as possible, including:

• email headers (From, Sent, To, Cc, Subject);
• inline images;
  NB; Currently, in GLPI version 11.0.8—unlike in earlier versions—images sometimes disappear after adding a follow-up via pasting.
• basic text formatting (paragraphs, lists, tables, fonts);
• spacing and line breaks; without introducing unwanted blank lines.

Why this matters:
Email exchanges often provide valuable context for understanding how an issue evolved or why a particular decision was made. Including the relevant part of an email in a ticket follow-up makes the ticket history more complete and easier to understand without having to consult external mailboxes.

Copying and pasting the relevant portion of an email is the most practical workflow because users can choose exactly which part of a conversation should be kept (typically from the From: header to the signature), while omitting earlier messages that are no longer relevant.

Alternative workflows, such as forwarding the email to GLPI's mail collector, are not suitable in this case. They are more cumbersome when several emails need to be added to an existing ticket, and they may also trigger unnecessary notifications to requesters, observers, or other recipients. For these reasons, improving the copy-and-paste experience would provide a simple and efficient solution for a common helpdesk task.