feat(next): glean emit view event

[StaberindeZA]

Because

• Record SubPlat P1 metric view event using glean

This pull request

• Adds payments-metrics library
• Adds PaymentsGleanManager to format events data and CMS data into the required format for Glean events recording.
• Adds PaymentsGleanService to handle metrics events emitted by Next.js
• Adds the manager and service to the NestApp
• Adds new config values to payments-next for Glean reporting
• Emit view event from Checkout start page

Issue that this pull request solves

Closes: #FXA-10087

Checklist

Put an x in the boxes that apply

• My commit is GPG signed.
• If applicable, I have modified or added tests which pass locally.
• I have added necessary documentation (if appropriate).
• I have verified that my changes render correctly in RTL (if appropriate).

[xlisachan]

Should this not be written as follows instead?:

# Set in next.config.js
GLEAN_CONFIG__VERSION=

[StaberindeZA]

The intention here is to show the developer that this config value exists, but that it's not set in any .env file, but instead is set in next.config.js. Leaving the comment on the same line as the config var, IMO more clearly indicates that the comment only applies to this line.

[xlisachan]

apps/payments/next/lib/metrics/glean/server_events.ts auto-generated when I pulled down the branch.

[StaberindeZA]

apps/payments/next/lib/metrics/glean/server_events.ts was the original location of server_events.ts so it might just be an artifact from before this PR.

If you delete the folder apps/payments/next/lib/metrics it should not be automatically created again.

[xlisachan]

I was able to start the stack and saw the event logged in payments-next.

I left a comment about a file that auto-generated and not listed in .gitignore and there are copyright header/import lines that are out of order in a few files. Otherwise, LGTM - thanks Reino!