Draft: Merge Request Widget for Generic Reports

What does this MR do and why?

This merge request collates the job artifacts introduced by !93357 (closed) and adds a merge request widget for it

How to set up and validate locally

1. Create a project containing the following .gitlab-ci.yml

build:
    image: busybox
    script:
        - echo "Done"
    artifacts:
        reports:
            generic: generic-one.json
test:
    image: busybox
    script:
        - echo "Test"
    artifacts:
        reports:
            generic: generic-two.json

and two json files: generic-one.json

[
    {
      "id": "MesOne",
      "header": "First Message",
      "text": "This is the text of the first message",
      "icon": {
        "name": "neutral"
      },
      "children": [
        {
          "id": "SubMesOne",
          "header": "This is the header of the submessage",
          "text": "SubmessageText",
          "icon": {
            "name": "severityCritical"
          }
        }
      ]
    }
]

generic-two.json

[
    {
      "id": "SecondMessage",
      "header": "Message Two",
      "text": "This is a second message"
    }
]

2. Create a merge request with any change that leaves these files intact
3. See the messages on the merge request widget

Screenshots

Still a bit clunky view if you add a link:

Open points

• Should collated messages overwrite each other? They do right now
• Should the messages be ordered by job they are from or flattened?
• Should we use the more generic MR Widget V2?
• Needs test for child pipelines
• Needs tests in general

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.