Add GraphQL PMG to MR widget

What does this MR do and why?

This is the first task for #419725

We are adding the GraphQL version of the pipeline mini graph to the MR widget in anticipation of the full migration coming up.

Screenshots or screen recordings

How to set up and validate locally

Prerequisites

• An enabled feature flag: Feature.enable(:ci_graphql_pipeline_mini_graph)
• A working runner

Steps

1. Navigate to a project (this example uses the flightjs group)
2. Navigate to the Pipeline Editor (Build > Pipeline editor)
3. Update the gitlab-ci.yml and enter a new branch name. Check the "start a new merge request with these changes" boxes
4. Create a merge request
5. You should see the graphql pipeline mini graph widget on the merge request page