When booking in the Calendar, implement a function to reserve the appointment so that it cannot be taken by someone else while being given

Mme Slight from gmfblainville contacted us with a request.
They seem to have had an incident of some incredibly unfortunate timing.
She managed to give a patient an appointment at the exact same time(down to the second) as someone took an appointment in the portal for Wednesday, August 02, 2023 in the calendar of Dr. Ibrahim, Julie.

They would like to request, if possible, a way to implement a "placeholder" function when in the appointment in the Calendar, like when you're buying tickets online, so that while you're booking, your booking can't be sniped by someone else.

– Affected user(s): Clinic staff
– Impact : The client has indicated to us that this situation has arisen several times before and this would likely be the best solution.
– Current state: Presently, if 2 users at the clinic are in the same booking before it has been completed, they can both assign it to a patient, which leads to being double booked. Also, a patient online is able to select the appointment at the same time as it is being booked in the clinic.