Frontend: New campaigns flow

Created by: eseliger

RFC: RFC 157 - Campaigns authorization model

Docs PR (including links to Figma): https://github.com/sourcegraph/sourcegraph/pull/10921 Backend issue: #10985 (closed)

Tasks

• Create new Figma mockup based on most-recent concept and get confirmation from product
• Ask Design if there are open questions or missing pieces
• Throw out old components
• Add stories for components that are retained
• Add campaign spec preview page
  • Visible changeset spec node
  • Hidden changeset spec node
• Campaign header
• Campaign status component
• Combined changeset list
• Tabbed changeset/burndown chart UI
• Campaign page on user/org site
• Changeset mode should support publication and reconciler state