#7467252 Add default payment block plan name

Proposed Changes

When adding a new payment plan for the Jetpack Payment Button block to
use, the plan name will update depending upon the payment options
selected – whether it’s a donation and what the payment frequency is.

This aids users in naming their plans appropriately. Making the form
faster to fill in accurately.

If the user explicitly chooses a name that differs from one of the
possible defaults, then that is respected and not overwritten.

Testing Instructions

1. Use the generated calypso preview link
2. On a site with a paid plan, go to Tools -> Earn in the menu
3. If you haven’t already, follow the CTA to connect Stripe
4. Use ‘Manage Payment Button’ button
5. In the ‘Manage Plans’ section click ‘Payment plans’
6. Press ‘Add a new payment plan’
7. Notice that the plan name is defaulted to Monthly Subscription
8. Notice that as you use the donation and renewal frequency controls that it updates the plan name
9. Enter a completely custom plan name, notice that using the donation and renewal frequency controls no longer updates the plan name

The below image shows the contents of the textbox with the title:

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 Automattic/jetpack#24074, it’s essentially the Calypso version of Automattic/jetpack#25397