Archive Label GraphQL endpoint

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What does this MR do and why?

Adds a GraphQL endpoint to update the archived attribute of labels.

This MR is a prerequisite for #554227 (closed). We need to add the API first, in order to be able to archive/unarchive the label from the frontend.

Labels in labels list

1. When a label is not archived, add an action from the Labels list "Archive". This should be the last action in the ellipsis menu.
2. When a label is archived, add an action from the Labels list "Unarchive". This should be the first action in the ellipsis menu.

🛠️ with ❤️ at Siemens

References

Issue: #4233

Screenshots

How to set up and validate locally

1. Enable feature flag with rails c:

 Feature.enable(:labels_archive)

2. Get the global label id from a label: Label.last.to_global_id
3. Use curl or the GraphQL explorer to mutate the label. Change id and archived in the variables:

curl --request POST \
  --url https://gdk.test:3443/api/graphql \
  --header 'Authorization: Bearer <glpat>' \
  --header 'Content-Type: application/json' \
  --data '{
  "query": "mutation labelUpdate($id: LabelID!, $archived: Boolean) {\n  labelUpdate(input: { id: $id, archived: $archived }) {\n    label {\n      id\n      archived\n    }\n    errors\n  }\n}\n",
  "operationName": "labelUpdate",
  "variables": {
    "id": "gid://gitlab/ProjectLabel/78",
    "archived": true
  }
}'

mutation labelUpdate($id: LabelID!, $archived: Boolean) {
  labelUpdate(input: { id: $id, archived: $archived }) {
    label {
      id
      archived
    }
    errors
  }
}

{
  "id": "gid://gitlab/ProjectLabel/780",
  "archived": true
}

MR acceptance checklist

checklist

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the javascript style guides
• Conforms to the database guides

Related to #4233