#4120774 Add warning notice in checkout when plan includes backup already

Changes proposed in this Pull Request

Customers who purchased a Backup product (monthly or real time) can have a duplicated backup feature by purchasing a Jetpack plan that includes it as well. This PR adds a warning for such cases in the checkout screen.

Testing instructions

1. No Backup
   • Select a Jetpack site that has no Backup
   • Go to _Plan > Plans
   • Select any of the 3 plans
   • Once in the checkout page, verify that you don’t see any notice and that there’s no error in the console
   • Repeat for the other plans
2. Backup Daily
   • Select a Jetpack site that has Backup Daily
   • Go to _Plan > Plans
   • Select any of the 3 plans
   • Once in the checkout page, verify that you do see a notice and that there’s no error in the console
   • Both links in the notice should redirect you to the Backup Daily purchase page
   • Repeat for the other plans
3. Backup Real-Time
   • Select a Jetpack site that has Backup Real-Time
   • Go to _Plan > Plans
   • Select any of the 3 plans
   • Once in the checkout page, verify that you do see a notice only for the Business plan
   • Both links in the notice should redirect you to the Backup Real-Time purchase page
   • Repeat for the other plans

Screenshots

Mockups

Implementation