feat: configure mail fetcher with offlineimap

- Use tags to help on the Qrexec policy notation;
- Create AppVMs also to fetch and send emails, useful for OfflineIMAP
  that requires sync;
- OfflineIMAP is smart enough depending on the server, such as Gmail;
- Quote options managed by the user such as password fields as they
  could contain spaces; and
- Default fetching method to always keep files on the remote to avoid
  users being surprised about the fetcher behavior or losing data.

salt/mail/files/fetcher/offlineimaprc.example

@@ -0,0 +1,29 @@
+# ~/.offlineimaprc
+
+## SPDX-FileCopyrightText: 2023 - 2025 Benjamin Grande M. S. <ben.grande.b@gmail.com>
+##
+## SPDX-License-Identifier: AGPL-3.0-or-later
+
+##### DO NOT EDIT THIS BLOCK #####
+[general]
+accounts = main
+[Account main]
+localrepository = main-local
+remoterepository = main-remote
+[Repository main-local]
+localfolders = ~/mail
+##### EDIT THIS BLOCK #####
+sync_deletes = no
+type = Maildir
+##### DO NOT EDIT THIS BLOCK #####
+[Repository main-remote]
+sslcacertfile = /etc/ssl/certs/ca-certificates.crt
+##### EDIT THIS BLOCK #####
+synclabels = yes
+readonly = yes
+sync_deletes = no
+type = IMAP
+remotehost = imap.mail.example
+remoteuser = john-doe@mail.example
+
+# vim: ft=toml