Add the ability to have a "sync" shutdown

[gquittet]

By default, the "closePromises" are executed in parallel.

Add a syncClose option that allow end-user to have a "sync" shutdown to execute promises in series.

Ex:

[() => Promise1, () => Promise2, () => Promise3]

With the actual behavior, the result can be random:

- Promise1
- Promise2
- Promise3

or

- Promise2
- Promise1
- Promise3

or

- Promise3
- Promise1
- Promise2

and so on.

The goal is now to have :

- Promise1
- Promise2 (when Promise1 is finished whatever the reason)
- Promise3 (when Promise2 is finished whatever the reason)

Also replace all Promise.all calls with Promise.allSettled to ensure all closePromises are called.