DF-1099: Notification banner component

[alexluckett]

Proposed change

Adds a NotificationBanner component to the plugin. Supports title, heading via options.heading and content via content. Heading and content support markdown (e.g. links, formatting).

Depends on DEFRA/forms-designer#1450.

Jira ticket: DF-1099

Type of change

• Bug fix
• New feature
• Breaking change
• Misc. (documentation, build updates, etc)

Checklist

• You have executed this code locally and it performs as expected.
• You have added tests to verify your code works.
• You have added code comments and JSDoc, where appropriate.
• There is no commented-out code.
• You have added developer docs in README.md and docs/* (where appropriate, e.g. new features).
• The tests are passing (npm run test).
• The linting checks are passing (npm run lint).
• The code has been formatted (npm run format).