Allow excluding group-level work items in group.workItems GQL field

What does this MR do and why?

Adds exclude_group_work_items parameter to WorkItems::WorkItemsFinder to match IssuesFinder behaviour, which will enable migrating the group-level issues list to use the work items API.

ETA: The parameter was included in a separate MR (!202865 (merged)), this one was updated to add the GQL argument and tests.

Changes:

• Add exclude_group_work_items param to WorkItems::WorkItemsFinder (defaults false). When true, filters out group-level work items, returning only project work items
• Add argument excludeGroupWorkItems to the GraphQL fields namespace.workItems and group.workItems

Database

• No new DB queries - reuses existing exclusion logic
• Same query plan as the current IssuesFinder group behaviour

WorkItems::WorkItemsFinder.new(current_user, { group_id: group.id, include_descendants: true, exclude_projects: false, exclude_group_work_items: true }).execute

exclude_group_work_items value	query plan
false	https://console.postgres.ai/gitlab/gitlab-production-main/sessions/42808/commands/131076
true	https://console.postgres.ai/gitlab/gitlab-production-main/sessions/42808/commands/131066

References

Related to #565433 (closed)

Screenshots or screen recordings

GraphQL request to fetch work items

Before	After

How to set up and validate locally

1. Create a group and a subgroup. Add a project in each level
2. Create a work item in each (requires enabling the flag create_group_level_work_items for the group-level work item)

createWorkItem

mutation createWorkItem {
  workItemCreate(input: {
    namespacePath: {group_path|project_path}, title: "Issue in {group_path|project_path}",
    workItemTypeId: "gid://gitlab/WorkItems::Type/1"
  }) {	
    workItem {
      id
      workItemType { name }
    }
    errors
  }
}

3. Use the following query with the different argument combinations to verify that group-level work items are excluded

getWorkItems

query getWorkItems($excludeProjects: Boolean, $includeDescendants: Boolean, $excludeGroupWorkItems: Boolean, $fullPath: ID!) {
  group(fullPath: $fullPath) {
    workItems(
      excludeProjects: $excludeProjects
      includeDescendants: $includeDescendants
      excludeGroupWorkItems: $excludeGroupWorkItems
    ) {
      nodes {
        title
      }
    }
  }
}

{
  "excludeProjects": false,
  "includeDescendants": true,
  "excludeGroupWorkItems": true,
  "fullPath": "root-group"
}

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