PMG query consolidation

What does this MR do and why?

Related to #465309 (closed) (spike) and #465561 (closed) (frontend issue)

We are consolidating the 2 top level queries of the pipeline mini graph.

Before - Pipeline stages populated with getPipelineStagesQuery, upstream and downstream pipelines populated with getLinkedPipelines.

After - All pipelines/statuses populated with one initial query.

There is no change in the UI and the code should function the exact same.

Most up-to-date version of the architecture blueprint. This blue print is published here.

Screenshot

How to set up and validate locally

Note: You should not be able to click on the pipeline mini graph stages. This MR is just for rendering the component initially.

This work is behind a feature flag ci_graphql_pipeline_mini_graph.

1. In the rails console, run Feature.enable(:ci_graphql_pipeline_mini_graph)
2. Navigate to a project with a pipeline
3. Navigate to Build >> Pipeline editor and insure that the pipeline mini graph has rendered.