Add status field information

[jthomperoo]

Is your feature request related to a problem? Please describe.
To help with debugging and to provide more context the CPA should give better information when reporting its status.

Describe the solution you'd like
The status should include these fields:

• lastScaleTime is the last time the CustomPodAutoscaler scaled the number of pods, used by the autoscaler to keep track of downscale stabilization between restarts.
• currentReplicas is the current number of replicas of pods managed by this autoscaler, as last seen by the autoscaler.
• desiredReplicas is the desired number of replicas of pods managed by this autoscaler, as last calculated by the autoscaler.
• currentMetrics is the last set of metrics gathered by this autoscaler, the last metrics gathered in the metric gathering stage
• currentEvaluation is the last evaluation decision retrieved by this autoscaler, the last evaluation decision retrieved in the evaluation stage
• reference is the identifier for the resource being scaled in the format <api-version>/<api-kind/<name>.

Of these fields only the reference could be populated by the operator, the rest would rely on the CPA itself updating them.

Along with these new status fields the CPA should also report some of this information as printer columns:

• Last Scale Time is the last time the CustomPodAutoscaler scaled the number of pods.
• Current Replicas is the current number of replicas of pods managed by this autoscaler.
• Desired Replicas is the desired number of replicas of pods managed by this autoscaler.
• Reference is the identifier for the resource being scaled in the format <api-version>/<api-kind/<name>.

Describe alternatives you've considered
N/A

Additional context
Would allow jthomperoo/custom-pod-autoscaler#168 to be implemented.