Support Universal Analytics and Google Analytics 4 IDs simultaneously

[chalin]

This is a proposed solution for:

• Support Google Analytics 4 (GA4) and migration to GA4 #1096

This PRs eases migration from UA to GA4 by allowing both IDs to be specified via the googleAnalytics configuration parameter.

I've proposed this change to the Hugo template here:

• Adds support for GA4 and UA at the same time gohugoio/hugo#10094

In the meantime, we might want to support a template override as given in the PR.

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For context, we're in the midst of migrating CNCF projects. For details see:

• Migrate CNCF websites to GA4 cncf/techdocs#108

/cc @nate-double-u

[chalin]

Set this as draft since I might have found a better way of dealing with migration that doesn't require more than one site tag ID. Will keep y'all posted of my progress, and either close or un-draft this PR accordingly.

[chalin]

After much thought, I'm going to close this. I don't want to propose a Docsy feature that runs the risk of not being adopted upstream. This solution of supporting multiple IDs simultaneously, while interesting, feels like a special case of a more general need of supporting general config gohugoio/hugo#4479.