[Ballista] Improve task and job metadata

[edrevo]

The task and job status we save in the scheduler state is currently lacking. See:

https://github.com/apache/arrow-datafusion/blob/16011120a1b73798049c5be49f9548b00f8a0a00/ballista/rust/core/proto/ballista.proto#L669-L680

And

https://github.com/apache/arrow-datafusion/blob/16011120a1b73798049c5be49f9548b00f8a0a00/ballista/rust/core/proto/ballista.proto#L614-L624

The job status should include:

• Start time for the job (the moment it was queued)
• Finish time for the job (for the completed state)
• Number of pending/running/completed/failed tasks and stages (for the running state)

The task status should include:

• Start time for the task
• Finish time for the task (for the completed state)

[edrevo]

cc @pradomota. I'm opening this one in case you want to take a stab at it 😉 We can do pair programming if you want.

[msathis]

This will be great addition. We can expose this information to the UI as well.