Move docs from event tracking to telemetry
Overview
This MR renames Event Tracking to Telemetry across docs.gitlab.com. This change is needed as the first step in writing the Telemetry Implementation Guide https://gitlab.com/gitlab-org/telemetry/issues/290.
Follow up MR to also update the navigation: gitlab-docs!739 (merged)
Parent issue: https://gitlab.com/gitlab-org/telemetry/issues/290
Edited by 🤖 GitLab Bot 🤖