[GA4] Fall back to Hugo's GA template

[chalin]

• Prerequisite:
  • Enable page feedback even without a Google analytics ID #1727
    which will allow us to drop bogus U-000000 IDs from project configs
• Revert the following once 1727 is solved, because I don't think that it's worth maintaining a override of an internal Hugo template (given that UA analytics have stopped working):
  • Use the gtag.js analytics library by default #1177

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To assess what has been updated since #1177 was merged, compare the following:

• https://github.com/gohugoio/hugo/blob/master/tpl/tplimpl/embedded/templates/google_analytics.html
• https://github.com/gohugoio/hugo/blob/f7e00c039ff3cea5f991b05c1e325666004cf129/tpl/tplimpl/embedded/templates/google_analytics.html

[chalin]

• Closed by Fall back to Hugo's default behavior for disableHugoGeneratorInject #1734