Add stackrank to fields list for batch fetch by id (#350)

Added stack rank to list of returned fields so that it can be used to
re-order a backlog easier

## GitHub issue number #349 

## **Associated Risks**

None

## ✅ **PR Checklist**

- [x] **I have read the [contribution
guidelines](https://github.com/microsoft/azure-devops-mcp/blob/main/CONTRIBUTING.md)**
- [x] **I have read the [code of conduct
guidelines](https://github.com/microsoft/azure-devops-mcp/blob/main/CODE_OF_CONDUCT.md)**
- [x] Title of the pull request is clear and informative.
- [x] 👌 Code hygiene
- [x] 🔭 Telemetry added, updated, or N/A
- [x] 📄 Documentation added, updated, or N/A
- [x] 🛡️ Automated tests added, or N/A

## 🧪 **How did you test it?**

Manual validation and re-ran tests

Author: danhellem

src/tools/workitems.ts

@@ -130,7 +130,7 @@ function configureWorkItemTools(server: McpServer, tokenProvider: () => Promise<
     async ({ project, ids }) => {
       const connection = await connectionProvider();
       const workItemApi = await connection.getWorkItemTrackingApi();
-      const fields = ["System.Id", "System.WorkItemType", "System.Title", "System.State", "System.Parent", "System.Tags"];
+      const fields = ["System.Id", "System.WorkItemType", "System.Title", "System.State", "System.Parent", "System.Tags", "Microsoft.VSTS.Common.StackRank"];
       const workitems = await workItemApi.getWorkItemsBatch({ ids, fields }, project);
 
       return {

test/src/tools/workitems.test.ts

@@ -285,7 +285,7 @@ describe("configureWorkItemTools", () => {
       expect(mockWorkItemTrackingApi.getWorkItemsBatch).toHaveBeenCalledWith(
         {
           ids: params.ids,
-          fields: ["System.Id", "System.WorkItemType", "System.Title", "System.State", "System.Parent", "System.Tags"],
+          fields: ["System.Id", "System.WorkItemType", "System.Title", "System.State", "System.Parent", "System.Tags", "Microsoft.VSTS.Common.StackRank"],
         },
         params.project
       );