refactor(create): clean up logic when prompting for unspecified arguments

[Josh-Cena]

Pre-flight checklist

• I have read the Contributing Guidelines on pull requests.
• If this is a code change: I have written unit tests and/or added dogfooding pages to fully verify the new behavior.
• If this is a new API or substantial change: the PR has an accompanying issue (closes #0000) and the maintainers have approved on my working plan.

Motivation

The create-docusaurus code is super messy, and because it's highly async and imperative, it's quite hard to refactor. Therefore, this refactor probably doesn't make the code any cleaner (😅), however, it aims to make the code more correct.

We get our input from two sources: CLI args, or prompt results. What happens when part of the arguments are provided from CLI, but we are missing information and need to prompt them? (e.g. yarn create docusaurus --git-strategy shallow) This PR will standardize the behavior in this case. (Previously, we would still prompt for the template, and would even accept classic—but in this case, we should really only accept a git repo URL)

What happens when you use a local template, and the local template contains a lockfile? We should definitely use the package manager for that, instead of still using heuristics. This PR fixes that behavior.

What happens when you enter a folder name as site name, but a path already exists? Previously, the process is aborted; now, it will simply reject the input and ask you to enter another.

What happens when you cancel the current prompt? Previously it would usually give a cryptic error, now it always correctly handles this case.

Test Plan

Tested locally

Test links

Deploy preview: https://deploy-preview-_____--docusaurus-2.netlify.app/

Related issues/PRs

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[github-actions]

⚡️ Lighthouse report for the deploy preview of this PR

URL	Performance	Accessibility	Best Practices	SEO	PWA	Report
/	🟠 67	🟢 100	🟢 100	🟢 100	🟢 90	Report
/docs/installation	🟠 82	🟢 99	🟢 100	🟢 100	🟢 90	Report

[github-actions]

Size Change: 0 B

Total Size: 811 kB

ℹ️ View Unchanged

Filename	Size
website/.docusaurus/globalData.json	52.3 kB
website/build/assets/css/styles.********.css	105 kB
website/build/assets/js/main.********.js	615 kB
website/build/index.html	38.8 kB

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