Add Web Vitals to Scaffold

[dainemawer]

This PR adds Googles Web Vital library to the scaffold.
This work is specifically for new projects that have no way of accurately tracking core web vitals.

web-vitals.js is ~1kb in size, and is rendered directly into the template, not included in the bundle.

Description of the Change

• Adds a new theme constant: TENUP_WEB_VITAL_TRACKING to hide functionality behind a flag
• Adds a new file called web-vitals.php in the includes folder
• Adds 3 new scripts to the footer - one being the web-vitals library, the other is a choice of 3 strategies to follow: custom analytics endpoint, Universal Analytics and Google Analytics 4.

Closes #131

Alternate Designs

Possible Drawbacks

• There will need to be some further tweaks to the functions depending on the scope and context of the project.
• Two of the strategies depend on Google Tag Manager being present on the window object.

Verification Process

1. Set the TENUP_WEB_VITAL_TRACKING to true
2. Verify that the script tags with id: tenup-web-vital-tracking and send-data-to-endpoint are present in the DOM.

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.

Changelog Entry

Added - Core Web Vitals partial to includes
Added - New Theme Constant: TENUP_WEB_VITAL_TRACKING for flagging the functionality

Credits

Props @dainemawer

[tylercherpak]

Hey @dainemawer

I think this is great 😄 😄

I have a couple of questions:

• Can we move the scripts into js files and enqueue them with wp_enqueue_scripts?
• Does this script itself affect the web vitals score? Does the act of measuring impact performance?

Thanks!

[joesnellpdx]

@dainemawer

I also think this is great!

Per #131, there needs to be updates to the readme and comment guidance in the php files.

Per inline or enqueuing - I feel like inline makes more sense the way you have it, but I'm open for discussion on that.

Also, if opted in - there should be guidance on using the information either for our own racking purposes or sending to 3rd party (via the scripts that are in place).

For clarity - we'd need access to google analytics to see the data? If so, is there a way to maybe update one of our tools (i.e. Support Monitor)?