Add gitlab username and name to the mutation response

What does this MR do?

It adds gitlab_username and gitlab_name fields to the import users from Jira graphql mutation

Example request

mutation {
  jiraImportUsers(input: {startAt: 1, projectPath: "flightjs/flight"}) {
    errors
    jiraUsers {
      jiraAccountId
      jiraDisplayName
      jiraEmail
      gitlabId
      gitlabName
      gitlabUsername
    }
  }
}

Example response

{
  "data": {
    "jiraImportUsers": {
      "errors": [],
      "jiraUsers": [
        {
          "jiraAccountId": "557058:0867a421-a9ee-4659-801a-bc0ee4a4487e",
          "jiraDisplayName": "Slack",
          "jiraEmail": null,
          "gitlabId": null,
          "gitlabName": null,
          "gitlabUsername": null
        }
      ]
    }
  }
}

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• [-] Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.

Related issue: #225212 (closed)