Add API to query MR list in monorepo mode

Related issue: https://jihulab.com/gitlab-cn/gitlab/-/issues/3147 | Subsequent MR: Add API to bulk merge MR list in monorepo mode

What does this MR do and why?

Add an API to query MR list in monorepo mode

GET /{project_path}/-/merge_requests/{mr_id}.json?serializer=monorepo

iShot_2023-08-21_17.57.55

Screenshots or screen recordings

The return value of this API is used to display on the new MR list widget:

How to set up and validate locally

1. Under the same Group, create multiple Projects

2. Create an MR in each Project, and these MRs meet the following conditions

   • have the same source_branch
   • have monorepo label

3. Call this new API:

   PROJECT_PATH=flightjs/Flight
   MERGE_REQUEST_ID=24
   YOUR_COOKIES_FROM_BROWSER='...'
   curl --location 'http://127.0.0.1:3000/$PROJECT_PATH/-/merge_requests/$MERGE_REQUEST_ID.json?serializer=monorepo' \
   --header 'Cookie: $YOUR_COOKIES_FROM_BROWSER'

   Expect the following result

   {
       "merge_requests_list_status": "can_be_merged",
       "other_merging_branch": null,
       "merged_by_user": null,
       "has_permission_to_merge": true,
       "merge_requests": [
           {
               "title": "Update file xxx",
               "path": "/flightjs/Flight/-/merge_requests/24",
               "merge_error": null,
               "mergeable": true,
               "state": "opened",
               "head_pipeline": {
                   "icon": "status_success",
                   "text": "已通过",
                   "label": "已通过",
                   "group": "success",
                   "tooltip": "已通过",
                   "has_details": true,
                   "details_path": "/flightjs/Flight/-/pipelines/581",
                   "illustration": null,
                   "favicon": "/assets/ci_favicons/favicon_status_success-8451333011eee8ce9f2ab25dc487fe24a8758c694827a582f17f42b0a90446a2.png"
               },
               "breadcrumbs": [
                   {
                       "text": "flightjs",
                       "href": "/flightjs"
                   },
                   {
                       "text": "Flight",
                       "href": "/flightjs/Flight"
                   }
               ],
               "approvals_given": 0,
               "approvals_left": 0
           },
       ]
   }

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.