app:scaffold based on github release instead of git branches

[ChillPC]

What does this PR do?

Permit to pull scaffolds based on release (PR related : kuzzleio/project-templates#3).

When directory already exist:

$ ts-node bin/run app:scaffold test2 --flavor 2

 🚀 Kourou - Scaffolds a new Kuzzle application

  ✖ Creating and rendering application files
    → Directory "test2" already exist

When no asset release with flavor name found:

$ ts-node bin/run app:scaffold test5 --flavor not-existing

 🚀 Kourou - Scaffolds a new Kuzzle application

  ✖ Creating and rendering application files
    → Scaffold for the flavor "not-existing" does not exist

How should this be manually tested?

In src/commands/app/scaffold.ts, replace:

https://github.com/kuzzleio/project-templates/releases/latest/download/${assetName}`);

with:

https://github.com/ChillPC/multi-release-test/releases/latest/download/${assetName}`);

for test and use flavor generic or iot-platform.

Other changes

Multi line commands for running the app when finishing scaffolding to ease copy paste.

Module node-fetch that should have a stable API.

Avoid deprecated Ubuntu version