Refactor initSite method in Site/index.js

[lhw-1]

What is the purpose of this pull request?

• Documentation update
• Bug fix
• Feature addition or enhancement
• Code maintenance
• DevOps
• Improve developer experience
• Others, please explain:

Overview of changes:

Removes the "pass-through" method of initSite in Site/index.js, and modifies cli/src/cmd/init.js to directly call the init method from Site/template.ts.

This was initially brought up by @tlylt in #2148 (comment here).

Anything you'd like to highlight/discuss:

The initTemplate function has been renamed to init, reason being that it was initially named initTemplate to differentiate it from the initSite method. Since we are removing initSite in this PR, we can change it to init.

Testing instructions:

Ensure that all markbind init methods still work.

These were all tested and confirmed to work locally:
markbind init
markbind init --template default
markbind init --template minimal
markbind init --convert

Proposed commit message: (wrap lines at 72 characters)
Refactor initSite method in Site/index.js

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Checklist: ☑️

• Updated the documentation for feature additions and enhancements
• Added tests for bug fixes or features
• Linked all related issues
• No unrelated changes

[jovyntls]

LGTM 👍

[itsyme]

Thanks for the work @lhw-1! LGTM!