[Implementation] Add integration tests to remote-vector-index-builder

[rchitale7]

Description

• End-to-end integration test that calls create_vectors_dataset, build_gpu_index, and upload_index in sequence, in run_tasks method.
• End-to-end integration test that calls _build API to trigger a build request, and monitors status using _status API. _status API can poll for the build until timeout - if timeout is reached or build fails, the test fails.

[krisfreedain]

Catch All Triage - 1 2

[Rajrahane]

Ref:
Override S3_ENDPOINT #47