Backport of docs: Fixing path for autoscaling/agent/source nav item into stable-website

[hc-github-team-nomad-core]

Backport

This PR is auto-generated from #12166 to be assessed for backporting due to the inclusion of the label backport/website.

The below text is copied from the body of the original PR.

---

What/Why

While working on a project consuming these docs, I found a sidebar nav item with a different path than its siblings. Confirmed it with some Nomad folks via Slack that the nav item should have a matching path so this PR makes that change and also:

• moves from website/content/docs/autoscaling/agent/source.mdx to website/content/tools/autoscaling/agent/source.mdx, so that it is in the same place as its siblings
• adds a nav item for this file in website/data/tools-nav-data.json, so it shows up in the Tools docs page sidebar
• in addition to prefixing the path with /tools, updates the nav item object to pass that value as href instead of path in website/data/docs-nav-data.json

Testing

• Go to https://nomad-git-docs-amb-nav-item-fix-hashicorp.vercel.app/docs
• Ensure the Autoscaling > Agent > source sidebar menu item has the correct link of: https://nomad-git-docs-amb-nav-item-fix-hashicorp.vercel.app/tools/autoscaling/agent/source
• Go to https://nomad-git-docs-amb-nav-item-fix-hashicorp.vercel.app/tools
• Ensure there is a Autoscaling > Agent > source sidebar menu item
• Click the menu item
• Ensure the correct page and content shows

[github-actions]

I'm going to lock this pull request because it has been closed for 120 days ⏳. This helps our maintainers find and focus on the active contributions.
If you have found a problem that seems related to this change, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.