Add link clickthrough tracking to Pages instructions

What does this MR do and why?

This MR adds Snowplow tracking to measure clickthrough events on Pages documentation links. This is a measure to control the performance of the new onboarding screen.

Note: This entire partial is soon to be replaced by the Pages Onboarding Wizard, so this is only a temporary measure to identify effects during a slow rollout.

Screenshots or screen recordings

This MR does not change the UI

MR acceptance checklist

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