Add-ons: Minor issues/improvements

[ankatiyar]

Description

Collecting stuff I found during bug bash related to the add-ons/tools workflow here -

Add ons info in pyproject.toml

This currently gets added to the project's pyproject.toml as a string -

add_ons = "['Linting', 'Custom Logging', 'Documentation']"

Could this be a list for easier analytics on Heap side -

add_ons = ['Linting', 'Custom Logging', 'Documentation']

Additionally, could the selection of "example pipeline" be included in this?

[merelcht]

Quickly discussed this and it would be nicer to have "example" as a separate entry.

[ankatiyar]

Also found this while testing -
kedro new --addons=lint,test,lint,test
or entering repeat numbers in the prompt does not fail but ends up adding this to the pyproject.toml:

add_ons = "['Linting', 'Testing', 'Linting', 'Testing']"