Add being able to export/show a list of vendor e-mail addresses

[akx]

User story

As an event's kirpputorivastaava, I want to be able to send an informative email to all vendors with items in said event.

Current situation

I need to resort to asking someone to manage.py shell to

print(
    "\n".join(
        sorted(
            Item.objects.filter(vendor__event__name="Desucon Frostbite 2024")
            .values_list("vendor__user__email", flat=True)
            .distinct()
        )
    )
)

or similar.