Change SSE routes structure

What does this MR do?

Contributes to #213282 (closed)

We want to extend route structure for Static Site Editor endpoint to support Vue routes.

Example: https://gitlab.com/[namespace]/[project]/-/sse/[editable]/[vueroutes].

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry (https://docs.gitlab.com/ee/development/documentation/workflow.html#when-documentation-is-required))
• Code review guidelines
• Merge request performance guidelines
• Style guides

Availability and Testing

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