Add CI minutes usage data to GraphQL

What does this MR do?

This MR adds fields and types for CI minutes usage data to GraphQL. All the code is added in EE to keep it in the same module as the rest of the CI minutes code, pending a future transition to Core in #336569 (closed)

• Adds QueryType.ciMinutesUsage
• Adds Ci::Minutes::NamespaceMonthlyUsageType
• Adds Ci::Minutes::ProjectMonthlyUsageType

Issue

This MR completes #332069 (closed), which is a blocker for the frontend implementation of the feature that will use this data in #246844 (closed)

Example GraphQL query and data