Use fs native API with promises

[LoicPoullain]

Issue

Some old code has been promisified in order to work with NodeJS API. In latest versions of Node, async functions are natively available with promises. Foal should use these functions directly instead.

Solution and steps

• Use node:fs/promises

Checklist

• Add/update/check docs (code comments and docs/ folder).
• Add/update/check tests.
• Update/check the cli generators.