Update mail_debug command to use aiosmtpd

[weslord]

Issue #1831

Python 3.12 dropped asyncore and smtpd

This adds a new dependency aiosmtpd from pypi. Should we add some kind of check and instructional message if the library is not found?

[jayvdb]

I think it would be useful to add additional tests - currently there is only one, which doesnt test that the server is doing smtp stuff.

And in the Command.handle, add something like

django-extensions/django_extensions/management/commands/export_emails.py

Lines 137 to 141 in 0e57475

	try:
	import vobject
	except ImportError:
	print(self.style.ERROR("Please install vobject to use the vcard export format."))
	sys.exit(1)

to check that aiosmtpd is installed.

[ulgens]

@weslord Any luck with the recommended changes? I can create a PR to help.