Make it possible to create project from config without providing add_ons or example_pipeline

[merelcht]

Description

Creating a project from config without providing add_ons or example_pipeline fails.

Context

config.yml:

project_name: My First Kedro Project
repo_name: testing-kedro
python_package: test_kedro

By itself, this doesn't work - throws the following error:

kedro.framework.cli.utils.KedroCliError: example_pipeline, add_ons not found in config file.
Run with --verbose to see the full exception

I would assume these would use the default values if not provided.

Expected behaviour

The above config yaml is valid and so project creation should succeed.

[SajidAlamQB]

Completed in: #3370