Expose issuesSettings GraphQL field

What does this MR do and why?

As part of the configurable work item statuses work, the frontend needs access to the issues settings path where configurable lifecycles and statuses are defined and managed.

This MR adds the issuesSettings field to the namespacesLinkPaths GraphQL API to provide easy access to that path.

Notes

• Configurable work item statuses are only available for groups and projects. issuesSettings returns nil for user namespaces, which are not yet supported.
• issuesSettings always returns a path for root-level groups, since lifecycles and statuses are defined at the root and cascade down to subgroups and projects.

References

• #554433 (closed)

Screenshots or screen recordings

Namespace	Screenshot
Root group namespace
Subgroup namespace
Project namespace
User namespace

How to set up and validate locally

1. Run the following query for the group, project and user namespaces to test the new issuesSettings GraphQL field.

query namespaceLinkPaths {
  namespace(fullPath: "flightjs/Flight") {
    id
    fullPath
    linkPaths {
      issuesSettings
    }
  }
}

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