Allow filtering by member relations in GraphQL

What does this MR do?

This exposes the filtering options from the members finders to GraphQL clients: you can filter by direct members, inherited members, descendant members, members from invited groups, or any combination of those.

For gitlab-com/gl-infra/scalability#685 (closed).

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)

Availability and Testing

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