Update Google Analytics only_pageview mode to GA4

[maple3142]

PR Checklist

• The commit message follows guidelines for NexT.
• The changes have been tested (for bug fixes / features).
• Docs in NexT website have been added / updated (for features).

PR Type

• Bugfix.
• Feature.
• Improvement.
• Code style update (formatting, linting).
• Refactoring (no functional changes).
• Documentation.
• Translation.
• Other... Please describe: Replace the usage of the to be depreacted Universal Analytics measurement protocol api with the new api. (source)

What is the current behavior?

The custom pageview sending code (will be used when only_pageview is enabled) is using the old measurement protocol api.

What is the new behavior?

Use the new GA4 measurement protocol api instead: https://developers.google.com/analytics/devguides/collection/protocol/ga4

• Link to demo site with this changes:
• Screenshots with this changes:

How to use?

Create a new Google Analytics 4 resource, and get api_secret according to the instruction described here.

In NexT _config.yml:

google_analytics:
  tracking_id: G-XXXXXXXXXX  # Measurement ID
  only_pageview: true
  measure_protocol_api_secret: # api secret

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All committers have signed the CLA.

[coveralls]

Pull Request Test Coverage Report for Build 4858498581

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 97.614%

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Totals
Change from base Build 4837883490:	0.0%
Covered Lines:	394
Relevant Lines:	399

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💛 - Coveralls

[r12f]

Will be nice if we could get this change up to date and in. The old GA is going away soon.

[ppodds]

@maple3142 Can you change this Pull request to open?

[ppodds]

@stevenjoezhang Could you merge this pull request? Old GA is already deprecated.

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