Static Site Editor: Create submit changes success page

What does this MR do?

It moves the view that displays a message when the user submits changes successfully to the /success page. It creates a guard that prevents navigating to the success page if changes haven‘t been submitted yet.

This MR does not deliver all the required changes to implement VueRouter in the editor. For the full list of Merge Requests and a detailed implementation plan, see #213282 (closed).

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content