Resolve "GDK error on non-unique GraphQL fragment 'PageInfo'"

What does this MR do?

CE counterpart: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/31532

Creates a folder graphql_shared to contain GraphQL queries/fragments/utils to share between Vue + GraphQL apps.

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

Closes #13330 (closed)