Migrate VSA duration charts from REST to GraphQL

We want to utilize GraphQL wherever possible across the VSA. We previously removed the reliance on Vuex for the duration charts in #498181 (closed), but now we need to convert the API requests to GraphQL to complete the conversion.

We will need to update DurationChartLoader to use GraphQL/Apollo instead of the current REST/Axios requests that are being used: https://gitlab.com/gitlab-org/gitlab/-/blob/55ad20b38f9e6db2062684349832c0fe4b6bbe7a/ee/app/assets/javascripts/analytics/cycle_analytics/components/duration_charts/duration_chart_loader.vue

This work was previously being completed via !180607 (closed), but was prevented due to necessary additions in the GraphQL API (related issue). Once the backend work is completed, the work in !180785 (closed) can be extended to complete this task.