Update DG to be consistent with default template

[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:

Updates the Onboarding Bootcamp to be consistent with changes made in #2225. Mainly wording and image updates to the Developer Guide.

Anything you'd like to highlight/discuss:

As the pageNav of the frontmatter in the default template was changed from 2 to 4, I've modified the instructions to accommodate this change: instead of changing it from 2 to 1, the readers are now expected to try changing it from 4 to 5, which will show the sub-headings in the panel. I've also included a "before" image for this section to better highlight the differences. Following this, should we include a before vs after for all the relevant sections?

Also, after the removal of title from site.json in #2128, the title property is not generated by default, so I've tweaked the wording to be more suitable (and included a panel to the site.json page in the UG for reference).

While #2282 is related, I will not tackle it in this PR (for now) as it is possibly being tackled in another ongoing PR.

Testing instructions:

Proposed commit message: (wrap lines at 72 characters)
Update DG to be consistent with default template

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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