Show N most recent actions by followed users

Requirements

• Show the N most recent activities across all of the current user's followed users
  • PM and UX are still deciding on the best value for "N". We can start with 10 for now, just please ensure it's easy to tweak later.
• Include all contribution events that we currently collect through the existing contribution event system
  • No need to add or remove anything from the current contribution event system - use what's already available
• Follow the visual design of the existing Activity page
• Follow the interaction patterns of the existing Activity page
• Maintain consistency with GitLab's design system
• Leverage the existing contribution event infrastructure