[Task]: Deploy new GA4 changes to addons-frontend

[abyrne-moz]

Description

Deploy codebase changes to addons-frontend dev

• Remove Universal Analytics (UA) completely — UA was sunset by Google in July 2024
  

• Migrate from direct gtag.js to Google Tag Manager (GTM) 
  

• Normalise all tracking event names to GA4 convention (lowercase_underscore)
  

• Remove utm_* query parameters from internal AMO links while preserving addonInstallSource for attribution
  

• External links (Firefox download, VPN, Extension Workshop) retain their UTM parameters
  

• Refactor sendEvent() to use GA4-style parameters (extension_name/theme_name, author, page_path, trusted) instead of UA-style action/label/value
  

• Remove web vitals custom code — GTM events will handle web vitals
  

• Add 5 new collection/hero tracking events
  

• Rename install-completion event categories to include _completed suffix
  

Acceptance Criteria

• New changes are deployed and reporting data correctly to GA4

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