Enable Reactive Scaling by supporting Application mode along with Session Cluster

To manage cloud costs effectively for customers, it is important to have reactive scaling across all sort of services residing in kubernetes. We have been active users of lyft's flink operator from the start and are extremely grateful for the operator's current features.

To enable reactive scaling in task managers from 0...n:
a) The operator has to support application mode cluster along with session mode.
b) The keda scaled object file has to be deployed by the operator and the trigger has to be externalized in the crd.

i and some members would love to contribute to this feature and some other pressing issues as well.

@anandswaminathan please let me know how to take this forward in terms of contribution .

Begin by reviewing how the operator currently handles session clusters and how its CRD represents scaling configuration. Define the application-mode behavior, operator-managed KEDA ScaledObject deployment, and CRD-based trigger configuration before implementation; done means reactive task-manager scaling from zero to n works for both cluster modes.

Written by the indexing model from the issue text.