Docs: Fix incorrect onboarding addon information

[GalacticAvenger]

Summary

Fixes incorrect documentation about the onboarding addon.

Fixes #32530

Changes

1. code/addons/onboarding/README.md: Updated to reflect that the onboarding addon is no longer included by default in new Storybook projects. The previous text incorrectly stated "This addon comes installed by default."
2. docs/configure/telemetry.mdx: Updated the "Storybook guided tour" link from the archived storybookjs/addon-onboarding repository to the current monorepo location at storybookjs/storybook/tree/next/code/addons/onboarding.

How to test

• Verify the README accurately describes the current installation behavior
• Verify the telemetry docs link points to the correct (non-archived) location

Summary by CodeRabbit

• Documentation
  • Clarified onboarding addon setup: it's no longer included by default in new projects and must be installed and registered manually.
  • Clarified how to manually trigger or retrigger the onboarding experience.
  • Updated documentation links to point to the current location of onboarding resources.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 4362e1bf-a08e-4fba-8720-91efbebe9ba0

📥 Commits

Reviewing files that changed from the base of the PR and between 3c1d16b and 4c1ab1a.

📒 Files selected for processing (1)

• code/addons/onboarding/README.md

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📝 Walkthrough

Walkthrough

Documentation updates: README now instructs installing/registering the onboarding addon and manually navigating to /?path=/onboarding; telemetry docs update a GitHub link target to the addon’s new location in the main Storybook repo.

Changes

Documentation Updates

Layer / File(s)	Summary
Onboarding README and telemetry link code/addons/onboarding/README.md, docs/configure/telemetry.mdx	Rewrites triggering instructions to remove default-inclusion claim, instructs installing/registering the addon and navigating to /?path=/onboarding; updates telemetry docs link to github.com/storybookjs/storybook/tree/next/code/addons/onboarding.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

✨ Finishing Touches

⚔️ Resolve merge conflicts

• Resolve merge conflict in branch fix/onboarding-addon-docs

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[jonniebigodes]

@GalacticAvenger thanks for taking the time to put together this pull request and helping us improve the documentation by catching these small issues. We appreciate it 🙏 ! I left one small item for you to look into when you're able.

Let me know once you've addressed it and I'll be more than glad to take another look and get it merged.

Have a fantastic day.

Stay safe

[github-actions]

	Fails
🚫	PR description is missing the mandatory "#### Manual testing" section. Please add it so that reviewers know how to manually test your changes.

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