#7889493 Plans 2023: update copy for sharing feature

Fixes Automattic/martech#1501

Proposed Changes

This PR is based on top of #74561.

• The current comparison grid contains 2 separate features: Limited shares in social media and Unlimited shares in social media. This change replaces these 2 features with a new feature, “Shares on social media” with plan-specific copy.

Note: String Freeze label will be added after the review is complete.

Testing Instructions

• Go to /start/plans and scroll down to the comparison grid.
• Confirm that under the “Growth and monetization tools” heading, the new feature is visible and matches the screenshot for both desktop and mobile.

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• 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)?
• 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)?