Create an IssueLink on workItem create mutation

What does this MR do and why?

Allows to mark a newly created work item as related to an issuable on the create work item mutation

How to set up and validate locally

1. Run bundle exec rails console
2. Run Feature.enable(:work_items)
3. Execute a GraphQL query like

mutation {
  workItemCreate(input: {projectPath: "Flightjs/flight", title: "test links on issue multiple", workItemTypeId: "gid://gitlab/WorkItems::Type/1", link: { workItemIds: ["gid://gitlab/WorkItem/100", "gid://gitlab/WorkItem/200"]}}) {
    workItem {
      title
      workItemType {
        id
        name
      }
    }
  }
}

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.

Related to #346042 (closed)