Optimize the limit of descendants

This issue will be divided into sub-issues, but the ultimate aim is to increase the limitation on the number of descendants when copying/moving/importing and creating elements.

To do this, we need to complete several steps before we can begin optimising the code.

# 0. Understanding our average requests numbers

It could be nice, if we could find the average user request from AWS for example.

# 1. Understanding our current limits

First of all, you need to be aware of the system's limitations. To do this, we will use loading tests.

- [ ] Find limits for the number of requests to obtain the home screen so that delays are acceptable
- [ ] Find limits for the number of descendants when copying items so that delays for other users (getting home screen, average requests) are acceptable
- [ ] Whats happen if users try to edit the item who is copying?

# 2. Understanding the bottleneck of limitation

Once we've found the limits on the number of descendants, we need to investigate and understand why we have this limit. Maybe we could do this step before finding the limits, or in parallel.

# 3. Define the purpose

We need to define the new limit we want to reach, i.e. the point at which we stop optimising.

# 4. Optimise the code

We can now optimise the code to increase the maximal number of descendants to the defined limit.

# 5. Validate the optimisation

We need to run the load tests again to validate that our optimisation is working properly, and to define new limits if there are any unknowns.