[14.0][IMP] export_async_schedule : Send attachments directly

[quoc-pn]

Improvement:

• Add the ability to specify mail template for export.async.schedule.

• Add the ability to attach the export attachment to the email.

These two new features will help if you want to send the export file to someone who doesn't have access to do (so they cannot open the link).

[OCA-git-bot]

Hi @guewen, some modules you are maintaining are being modified, check this out!

[github-actions[bot]]

There hasn't been any activity on this pull request in the past 4 months, so it has been marked as stale and it will be closed automatically if no further activity occurs in the next 30 days. If you want this PR to never become stale, please ask a PSC member to apply the "no stale" label.