Frontend: Pass dropdown_path of a pipeline stage through GraphQL

Follow up for #337514 (comment 695703971)

The only data we're missing is the dropdown_path. For now I'm just building it manually on the frontend, but ideally I think we should expose it so it can be fetched from graphql. This can be done as a follow-up but will need some help from backend

We want to avoid building URLs manually in the frontend and, for the pipeline editor, we want to avoid using REST endpoints to fetch data as well. To display the pipeline mini graph in the pipeline editor, we should expose the dropdown_path of a pipeline stage in GraphQL.

This is currently being used by pipeline_editor_mini_graph.vue and commit_box_pipeline_mini_graph.vue.

Implementation Table

Group	Issue Link
frontend	👈 You are here
backend	Backend: Add ciPipelineStage to GraphQL QueryType (#406278 - closed)