Add ContainerState to SidecarState

[danielhelfand]

Related issue is tkn taskrun describe, doesn't show any sidecar info #655 in the CLI repository.

The gist of the issue is that tkn tr desc doesn't show any information about sidecar containers that are part of a TaskRun. It would be nice to be able to show as part of a TaskRun description the name and state of the sidecar container.

This would also provide more information via a kubectl describe taskrun command.

The problem is that the SidecarState struct only has Name and ImageID at this time. It would be great to add the ContainerState similar to what is done for StepState.

Expected Behavior

I should be able to see the status of sidecar containers that are part of a TaskRun similar to steps.

Actual Behavior

Only the Name and ImageID are available under the Status of a TaskRun.

Additional Info

Original pr to introduce this was #1515

[danielhelfand]

/assign