Admin: Allow for scheduling of meetups for in-person or online groups

Allow for scheduling of meetups for in-person or online groups by an admin
Should send email to everyone in the group
Email should contain calendar invite and details about the event like an .ics ([example](https://github.com/opportunity-hack/evs/blob/a4a2b176bf00855e22a6466117b17ac0774adbed/app/routes/resources%2B/event-register.tsx#L175))