Docs: Revert naming changes for Event tracking

Parent issue: https://gitlab.com/gitlab-org/telemetry/issues/290

What does this MR do?

There was a suggestion we should revert this naming change back to how it was as it presents a false impression that it belongs to ~"group::analytics". With no further feedbacks, I think it makes sense to revert the renaming as I don't have a strong feeling that the renaming was necessary.

Related issues

• #37303 (closed)
• gitlab-docs!713 (comment 290507081)
• !25410 (merged)

Author's checklist

• Follow the Documentation Guidelines and Style Guide.
• If applicable, update the permissions table.
• Link docs to and from the higher-level index page, plus other related docs where helpful.
• Apply the documentation label.

Review checklist

All reviewers can help ensure accuracy, clarity, completeness, and adherence to the Documentation Guidelines and Style Guide.

1. Primary Reviewer

• Review by a code reviewer or other selected colleague to confirm accuracy, clarity, and completeness. This can be skipped for minor fixes without substantive content changes.

2. Technical Writer

• Optional: Technical writer review. If not requested for this MR, must be scheduled post-merge. To request for this MR, assign the writer listed for the applicable DevOps stage.

3. Maintainer

1. Review by assigned maintainer, who can always request/require the above reviews. Maintainer's review can occur before or after a technical writer review.
2. Ensure a release milestone is set.
3. If there has not been a technical writer review, create an issue for one using the Doc Review template.