feat(perf): Update onPostBuild step to generate performance on-boarding docs

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This pull request extends the wizard onboarding documentation generation such that we generate Performance onboarding documentation content as sub-steps.

We aim to provide Performance onboarding content for JavaScript and React projects. They'll be shown in the product like this:

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Related to #3226

I intentionally did not provide any meta-documentation for how to write and contribute content to the Performance onboarding checklist at @imatwawana 's wishes; since we're only providing content for JavaScript and React platforms in the short-term to validate this feature.

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🔍 Inspect: https://vercel.com/sentry/sentry-docs/39KV7NbHrzmNLLLK9ZB9ofbTV27o
✅ Preview: https://sentry-docs-git-performance-onboarding.sentry.dev

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Name	Status	Preview	Updated
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@AbhiPrasad @lobsterkatie I've added you both as reviewers. Can either/both of you take a look at the Performance onboarding documentation content I've added in this PR, and see if I'm on the right track?

These content will be displayed into the product in the form of a checklist; similar to how we serve wizard onboarding docs.

[AbhiPrasad]

Can we add a note to src/wizard in a markdown file explaining how this all works?

[imatwawana]

I've fixed some minor wording issues, but I've also left some questions.

[imatwawana]

I'm not sure if this is correct. The enable tracing snippet on the performance page is slightly different. This identical snippet is found at:
https://docs.sentry.io/platforms/javascript/#install

This applies to all of these files.

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@imatwawana I plan to use the doc_link attribute to place a link to the Performance setup pages on the Performance onboarding checklist.

Although the content is slightly different here, I wanted to provide the complete setup instructions without assuming the user has installed any dependencies beforehand.

[imatwawana]

Is there a specific reason we're using heading level 4 here? Is there a reason it isn't level 2? This applies to all of these files.

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@imatwawana This was intentional so that we have the "right" header sizing that fits well with the inserted checkboxes:

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@imatwawana @AbhiPrasad Can either of you take a look at this pull request again? I'm fairly happy with the changes so far that I'd like to land this into master branch.

This change should have no impact to either the primary Sentry documentation website, or the Sentry product.

The product feature that will consume the changes introduced in this pull request is being developed in getsentry/sentry#33852. Thus, this pull request is a dependency of the developing Performance onboarding checklist feature.