Document Security and Licence Management features permissions

There's nothing in https://gitlab.com/help/user/permissions regarding Security Dashboard, vulnerability dismissals, license management (who can approve/blacklist/list), etc.

We must update this page accordingly.

• Security
  • View Security reports (MR widget + pipeline)
  • Dismiss vulnerability
  • Create issue from vulnerability (should be the same as "Create new issue", but repeting doesn't hurt)
  • View Security dashboard
• License Management
  • View reports (MR widget + pipeline)
  • View blacklisted/approved licenses (only Developers should see the red cross or the green ticks in the list)
  • Approve/Blacklist license
  • View project status (Project settings)

/cc @bikebilly