Makes the security dashboard empty state a scoped slot

What does this MR do?

This adds a scoped slot to the security dashboard for the empty state.

Doing this allows us to have context-specific empty states for all the different places we use the dashboard.

I've also set up those context-specific states in accordance with the copy in issue #13979 (closed)

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Performance and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

#13979 (closed)