For spark operator with `track_driver_via_k8s_api`, detect driver completion by container status rather than pod phase

## Problem

`SparkSubmitOperator` with `track_driver_via_k8s_api=True` detects job completion by watching `pod.status.phase`. This breaks in two ways when the driver pod has sidecar containers:

1. The pod phase stays `Running` after the driver container exits (because the sidecar is still alive), so the poll loop never sees `Succeeded` and waits indefinitely.
2. On the `Failed` branch, `container_statuses[0]` is used to extract the exit code and reason — but index 0 is not guaranteed to be the driver container in a multi-container pod.

## When it occurs

Only when Istio (or another sidecar container like fluentbut) is injected into the **driver pod**.

## Proposed fix

Filter `container_statuses` by the driver container name (`spark-kubernetes-driver` is the Spark default) instead of relying on `pod.status.phase` or index 0:

- Treat the driver container's `state.terminated.exit_code == 0` as success.
- Treat `exit_code != 0` as failure, with the actual exit code and reason in the error message.
- Fall back to `pod.status.phase` if the container name is not found (defensive).

The driver container name could be made configurable via a new `k8s_driver_container_name` parameter defaulting to `spark-kubernetes-driver`.

## Workaround

Set `execution_timeout` on the operator. This is documented in the requirements section of the operator docs.

## Related

Introduced in: #67715