Fix global nav for internal analytics docs

What does this MR do and why?

This MR fixes the global nav to reflect the recent changes to Service Ping and Snowplow docs - nesting them within Internal analytics. The nav hasn't been updated and didn't highlight the active page for these docs.

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How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Configure a local GitLab Docs environment: https://gitlab.com/gitlab-org/gitlab-docs/-/blob/main/doc/setup.md.
2. Go to Contribute docs -> Contribute to GitLab -> Feature development -> Internal analytics -> any page in Service Ping or Snowplow
3. Validate that the pages now are kept highlighted properly in the nav.

Merge request acceptance checklist

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