Add driver information to the application status

[razvan]

Description

Tools (most notably Airflow) that manage the lifecycle of SparkApplications need to be able to monitor the logs of the application driver.

Currently there is no reference to the driver Pod from the application, which makes the task from above more cumbersome than it should be.

The operator should include such a reference in the SparkApplication status, to enable tools like Airflow's Kubernetes sensor to work out of the box.

Investigate if it's possible to persist logs from k8s executors and spark pods and update the the documentation page accordingly.