#10658560 Add/gifts front-end

Fixes Automattic/gold#272

Proposed Changes

• Add UI to gift a subscription from the subscriber list

Testing Instructions

“Gift subscription” menu

• Open calypso via the calypso live link below
• Go to a site with gifts module enabled
• Go to the subscribers page /subscribers/SITE_URL
• You should see the “Gift subscription” menu

Make sure the menu is not displayed when the module is disabled

• Disable or go to a site with the gifts module disabled
• Go to the subscribers page /subscribers/SITE_URL (make sure you are still on the live Calypso site)
  -> Make sure the menu “gift menu” is not displayed

Gift works

• Open calypso via the calypso live link below
• Go to a site with gifts module enabled
• Go to the subscribers page /subscribers/SITE_URL
• Free subscribe to your site and login with this use rot WPCOM
• Gift this plan
• Make sure you can see the Gift via CLI

 wp memberships gifts list --gift-user=USER_EMAIL SITE_URL
Environment: SANDBOX MODE ENABLED - Viewing test data

Site ID:     [edited]
Site Domain: SITE_DOMAIN
Site URL:    SITE_URL
User ID:       [edited]
User Login:    [edited]
User Email:    [edited]
+---------+-----------+---------+------------+
| gift_id | user_id   | plan_id | is_deleted |
+---------+-----------+---------+------------+
| 64      | [edited] | [edited]       |            |
+---------+-----------+---------+------------+

• Make sure you can now access the posts as a paid-subscriber
• Go to the user subscriptions: http://calypso.localhost:3000/read/subscriptions
• Make sure you see the gift label

Environment: SANDBOX MODE ENABLED - Viewing test data

Site ID:     [edited]
Site Domain: [edited]
Site URL:   [edited]
User ID:       [edited]
User Login:    [edited]
User Email:    [edited]
Subscriptions:[edited]
Success: No gifts found.

Error handling

• Try to gift a user the same plan a second time
• The right message should be diplayed

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• https://wpcalypso.wordpress.com/devdocs/docs/testing/index.md 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)?
• For changes affecting Jetpack: Have we added the “[Status] Needs Privacy Updates” label if this pull request changes what data or activity we track or use (p4TIVU-ajp-p2)?