Adds support for GA4 and UA at the same time

[chalin]

During migration from Universal Analytics (UA) to Google Analytics 4 (GA) it is useful to be able to configure both site tags at the same time. This PR adds the ability to specify a site tag list.

• Closes Update Google Analytics internal template to new style(gtag.js) #4327
• Closes why template google_analytics_async not support google v4? #8549
• Closes Google Analytics 4 config: no need for anonymize_ip parameter #10093

(I experimented with multiple solutions and the one propose here seems the least obtrusive and most backwards compatible).

/cc @jmooring @nate-double-u

[CLAassistant]

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[chalin]

• I'm going to close this in favor of proposing a broader solution which also encompasses Update the internal GA template #4479
• I'll also file a separate fix for Google Analytics 4 config: no need for anonymize_ip parameter #10093

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