Remove ci_graphql_pipeline_mini_graph

What does this MR do and why?

Resolves #499562

• Removed references to ci_graphql_pipeline_mini_graph
• Consolidated <legacy-pipeline-mini-graph> and <pipeline-mini-graph>
• Relocated shared components
• Removed the README as it is no longer needed

Screenshots or screen recordings

No UI change

How to set up and validate locally

Insure that the following pipeline mini graphs are functional:

• Pipelines page
• Commit page: pipeline summary and pipelines tab
• Pipeline editor: pipeline summary
• Merge request page: pipeline summary and pipelines tab