Create a helper function to poll for knowledge base indexing completion

[ommistry2914]

• Add convenience helpers on IndexingJobsResources and AsyncIndexingJobsResource to poll an indexing job until it reaches a terminal state.

• Method : wait_for_completion(uuid, timeout=300, poll_interval=2, raise_on_failure=True) (sync) and the same async signature on the async resource. They call retrieve() repeatedly, return the final IndexingJobRetrieveResponse on success, raise RuntimeError for failure/cancelled/error states when raise_on_failure=True , and raise TimeoutError if the timeout elapses. Removes the need for callers to write manual polling loops.

fixes #41

[bbatha]

Closing as a dupe of #49