Rename VSA StageSummary class

What does this MR do?

Pays technical debt. Renames the class and removes duplicated code.

Screenshots (strongly suggested)

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

Related to #217944 (closed)