search: Fix "search again" checkboxes
Created by: fkling
As reported in slack, clicking any of the labels was always selecting the first one. That's because we use the same ID for all checkboxes and labels are associated with checkboxes via ID.
This PR fixes it by appending an index to the ID to make it unique.
Test plan
Updated unit test.
Manual verification by executing https://sourcegraph.com/search?q=context:%40sourcegraph/all+record&patternType=literal locally, verifying that multiple checkboxes are rendered and selecting each by clicking on the label.
App preview:
Check out the client app preview documentation to learn more.