Save emails and templates

### Problem

I need to save mails to archive them in archive folders
And sometimes save emails drafts as templates, to reuse them

### Proposal

Save As button (and "Ctrl-S" shortcut) to save emails as.

Save As dialog could offer email and email template formats. "Msg" is a common one, and could be enough for both
Outlook supports templates as "OFT". I am not sure about thunderbird.

### Prior Art (Optional)

_No response_