feat: add a prompt to modify users .gitignore (closes netlify#2038)

[ngonsoto]

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Summary

Fixes #2038

Edits to .gitignore file are not shown to the user. This PR adds a prompt if the .netlify folder is not found in the .gitignore file and asks the user if it wants to add it.

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[lukasholzer]

@ngonsoto Thank you very much for your PR and taking the time to enhance our CLI!
I want to apologize upfront for being so late with my review 😬

From a consumer perspective there is no reason why the .netlify folder should not be added to the .gitignore, or at least we don't want to promote it. As all our build outputs are there and they should not be committed.

So the user input here would be in 99% the cases a "yes" – I think we can drop it for a better user experience and instead providing a meaningful log message that we adapted the users .gitignore which is stated as solution inside the issue:

Describe the solution you'd like

When the CLI modifies .gitignore we should print a log message reflecting the change to the user

Furthermore a prompt would cause issues on the link command in the CI so we would need to adapt it with a flag to pass without asking. The simpler and better approach in my humble opinion is to informing the user.

Therefore can you please update the PR with a log message?

[ngonsoto]

Hi @lukasholzer, no problem. I'll be updating the PR with the requested changes.

[lukasholzer]

Suggested change

	log('Adding local .netlify folder to .gitignore file...')
	log('Adding local .netlify folder to .gitignore file.')

[lukasholzer]

Awesome! Thank you very much for going over and adapting the PR 🌟