Create, Build, and Style > Broadcast messages

This issue is to complete the ~"pajamas::create", pajamasbuild, ~"pajamas::style" portion of ~"component::broadcast-messages" as part of FY20-Q2 OKR to Improve the quality and consistency of our UI.

This includes a single-source-of-truth component that is implemented in Vue and thoroughly documented on design.gitlab.com. This does not include implementing the component throughout the product.

Related epics:

• Components of Pajamas Design System
• Pajamas component: Broadcast messages

Related issues:

• FY20-Q2 UX OKR: Improve the quality and consistency of our UI

Checklist

• Usage documentation is included in Pajamas
• Design specs are included in Pajamas
• Component is built and styled in gitlab-ui according to specs
• Banner on vue tab that warns of incorrect styling is removed from Pajamas
• All demos and todos are complete
• Status is changed to Built in Pajamas
• Add a reference and link to the completed component in the Engineer Week in Review doc