Improve the in-app CI minutes purchase flow

After we move the CI minutes purchase flow into the app via #222517 (closed) we can start working on improving it. Potential improvements:

• save credit card info
• save billing address
• use Pajamas components
• make the flow easier and quicker to complete by using a modal

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Our goal is to maximise repeat purchases: an existing customer should be able to buy additional CI minutes with only 4 clicks.

Related:

• Emily's prototype for in-app pro-rated seats purchase
• Emily's wireframes

Early-stage mockups of the flow

Mural

The flow as outlined above takes 3 clicks to complete when an existing credit card is stored.

Questions:

• Do we need to tell the user which credit card it is? For example: Credit card ending with 5021
• Do we need to allow the users to change the credit card when an existing one is present?
• Do they need to accepts the T&Cs every time they buy minutes?
• How will this flow work/look like on mobile devices?