Rename instance_statistics_measurements in GraphQL QueryType

Problem to solve

In %13.10, we renamed the instanceStatisticsMeasurements node to usageTrendsMeasurements. The API docs shows the deprecation: https://docs.gitlab.com/ee/api/graphql/reference/index.html#queryinstancestatisticsmeasurements

Proposal

@Quintasan proposed in an MR: "create a follow-up issue to rename instance_statistics_measurements in app/graphql/types/query_type.rb to reflect this change".

• Announce the deprecation: !79429 (merged)
• Note the deprecation in the documentation
• Remove remaining references to instanceStatisticsMeasurements in the next major release