Add web vitals monitoring and integrate with GA4

[acrollet]

Note: Delete the description statements, complete each step. None are optional, but can be justified as to why they cannot be completed as written. Provide known gaps to testing that may raise the risk of merging to production.

Are you removing, renaming or moving a folder in this PR?

• No, I'm not changing any folders (skip to TeamSites and delete the rest of this section)
• Yes, I'm removing, renaming or moving a folder

If the folder you changed contains a manifest.json, search for its entryName in the content-build registry.json (the entryName there will match).

If an entry for this folder exists in content-build and you are:

1. Deleting a folder:

   1. First search vets-website for all instances of the entryName in your manifest.json and remove them in a separate PR. Look particularly for references in src/applications/static-pages/static-pages-entry.js and src/platform/forms/constants.js. If you do not do this, other applications will break!
      • Add the link to your merged vets-website PR here
   2. Then, Delete the application entry in registry.json and merge that PR before this one
      • Add the link to your merged content-build PR here

2. Renaming or moving a folder: Update the entry in the registry.json, but do not merge it until your vets-website changes here are merged. The content-build PR must be merged immediately after your vets-website change is merged in to avoid CI errors with content-build (and Tugboat).

⚠️ TeamSites ⚠️

Examples of a TeamSite: https://va.gov/health and https://benefits.va.gov/benefits/. This scenario is also referred to as the "injected" header and footer. You can reach out in the #sitewide-public-websites Slack channel for questions.

Did you change site-wide styles, platform utilities or other infrastructure?

• No
• Yes, and I used the proxy-rewrite steps to test the injected header scenario

Summary

• (Summarize the changes that have been made to the platform)
• (If bug, how to reproduce)
• (What is the solution, why is this the solution)
• (Which team do you work for, does your team own the maintenance of this component?)
• (If using a flipper, what is the end date of the flipper being required/success criteria being targeted)

Related issue(s)

• Link to ticket created in va.gov-team repo
  department-of-veterans-affairs/va.gov-team#0000
• Link to previous change of the code/bug (if applicable)
  department-of-veterans-affairs/vets-website#0000
• Link to epic if not included in ticket
  department-of-veterans-affairs/va.gov-team#0000

Testing done

• Describe what the old behavior was prior to the change
• Describe the steps required to verify your changes are working as expected
• Describe the tests completed and the results
• _Exclusively stating 'Specs and automated tests passing' is NOT acceptable as appropriate testing
• Optionally, provide a link to your test plan and test execution records

Screenshots

Note: This field is mandatory for UI changes (non-component work should NOT have screenshots).

	Before	After
Mobile
Desktop

What areas of the site does it impact?

(Describe what parts of the site are impacted if code touched other areas)

Acceptance criteria

Quality Assurance & Testing

• I fixed|updated|added unit tests and integration tests for each feature (if applicable).
• No sensitive information (i.e. PII/credentials/internal URLs/etc.) is captured in logging, hardcoded, or specs
• Linting warnings have been addressed
• Documentation has been updated (link to documentation *if necessary)
• Screenshot of the developed feature is added
• Accessibility testing has been performed

Error Handling

• Browser console contains no warnings or errors.
• Events are being sent to the appropriate logging solution
• Feature/bug has a monitor built into Datadog or Grafana (if applicable)

Authentication

• Did you login to a local build and verify all authenticated routes work as expected with a test user

Requested Feedback

(OPTIONAL) What should the reviewers know in addition to the above. Is there anything specific you wish the reviewer to assist with. Do you have any concerns with this PR, why?