Migrate @newrelic/next into repo

[jsumners-nr]

See #2123.

Note: we should mark it as experimental in the release notes and as an on-going basis.

Tasks:

• deprecate the @newrelic/next package
• Update lib/instrumentations.js to register a relative folder
• Remove the external versioned tests configuration.
• update tests to use test/lib/agent_helper instead of @newrelic/test-utilities
• Convert git history with the previous repo.
• Archive old repo when done.

[workato-integration]

https://new-relic.atlassian.net/browse/NR-256230

[bizob2828]

This is fine but I think we should wait to do this until we've deemed our instrumentation stable

[bizob2828]

If we do this, it's more than just migrating the next.js instrumentation into the repo. We had a bunch of FAQs around Next.js nuance and would have to port those and the standalone to externalize libraries