Resolve "Rename Design Management .graphql files to follow snake_case"

Currently, part of the GraphQL queries/mutations/fragments files uses camelCase for their names. To make them consistent with the common GitLab file naming convention, we would need to rename them to snake_case

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines

Closes #217714 (closed)