## Why
The current way of creating and deleting simulations doesn't scale for big instances. We cannot generate 50 simulations every time a guest confirms attendance, and we should not delete existing valuable simulations. For example, if a guest confirms attendance and declines right after, previously generated simulations should still be valid.
## What
In this PR we are introducing a series of changes that make simulations management easier:
1. We're removing the automatic creation of simulations.
2. Simulations are not removed anymore, neither manually nor automatically.
3. A new endpoint has been defined to create simulations on demand.
4. A digest property has been defined to determine whether a simulation is still valid (meaning there have not been any change in the list of guests involved).
Reviewed-on: #222
Co-authored-by: Manuel Bustillo <bustikiller@bustikiller.com>
Co-committed-by: Manuel Bustillo <bustikiller@bustikiller.com>
