Migrate broadcast messages page

What does this MR do and why?

Migrate broadcast messages page

• Migrates headline to use the page_heading component
  • Adds the ability to pass plain text to description
• Migrates gl-new-card to the new CRUD component
  • Aligns table items to baseline
  • Migrates actions to use tertiary buttons

MR acceptance checklist

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How to set up and validate locally

Related to #457239 (closed)