#7652835 Allow launchpad checklist to display warning icons

Some steps might need to show a warning to get attention.

Proposed Changes

• Allow launchpad checklist to show a warning for certain steps

Testing Instructions

• Checkout this branch
• yarn run start
• Go to http://calypso.localhost:3000/setup/newsletter
• Run through the process until you see the launchpad
• Make the plan_selected step in client/landing/stepper/declarative-flow/internals/steps-repository/launchpad/tasks.tsx have completed: false, warning: true
• Refresh the page
• Notice that an exclamation mark is displayed next to the Choose a Plan step

Before	After

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)?
• 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)?

Related to Automattic/dotcom-forge#1227