#7581303 Onboarding Standalone Installation: Add new feature flag

Proposed Changes

• Add new jetpack/standalone-plugin-onboarding-update-v1 feature flag for the new onboarding standalone installation.
• Add new copy to provide sample usage for the new feature flag.

Testing Instructions

1. • Run git fetch && git checkout add/onboarding-standalone-installation-feature-flag
   • Run yarn start
2. Go to http://calypso.localhost:3000/checkout/jetpack/thank-you/licensing-manual-activate-instructions/jetpack_backup_t1_yearly?flags=jetpack/standalone-plugin-onboarding-update-v1 or use the Calypso cloud live link and goto /checkout/jetpack/thank-you/licensing-manual-activate-instructions/jetpack_backup_t1_yearly?flags=jetpack/standalone-plugin-onboarding-update-v1.
3. Confirm the header displays Ok, let’s install Jetpack Backup.

Pre-merge Checklist

• Have you written new tests for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• Have we added the “[Status] String Freeze” label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?

Related to 1203097885147382-as-1203159154260050

• To see the specific tasks where the Asana app for GitHub is being used, see below:
  • https://app.asana.com/0/0/1203159154260048
  • https://app.asana.com/0/0/1203159154260050