test: fix batch move modification e2e test

[pedesen]

Description

This stabilizes the batch move modification e2e test.

Root cause

• After the migration is triggered, FE polls for /api/batch-operations to check if the operation is finished
• After the operation is finished, FE fetches the statistics once from api/process-instances/statistics
• In some cases the operation is finished, but the statistics data is not updated yet on BE side, so FE fetches old statistics
• In the test there is an assertion that statistics badges in the diagram are updated accordingly
• In the test the updated data is not fetched and the badges are showing the old data.

In the e2e test we had a mechanism which is supposed to refresh the page every 2 seconds, which didn't work properly

   await expect
      .poll(
        async () => {
          await page.reload();
          ...
        },
        {intervals: [2000], timeout: 30000},
      )
      .toBe(...);

Solution

Instead of trying to refresh the page until the data is visible in the UI, there is now a polling on the /api/process-instances/statistics API endpoint to ensure data is updated, followed by the assertion on the statistics badges in the UI.

Outcome

The batchMoveModification.spec.ts passed in the following test runs:

• 8/8 times: https://github.com/camunda/camunda/actions/runs/9517924498
• 3/3 times: https://github.com/camunda/camunda/actions/runs/9579236532/

Related issues

closes #18149

[vitorwtavares]

This doesn't seem like it was easy to debug, great job! 😄