Use a k8s cached client for the branch planner implementation

[luizbafilho]

We should use a Kubernetes cached client to optimize terraform objects query since that could potentially put a lot of pressure on k8s API.

This a follow-up issue of #779 derived by Michael comment: #790 (comment)

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User Story

As a Terraform Controller user,
I'd like to use a Kubernetes cached client for Terraform objects query in the branch planner implementation,
so that it reduces the pressure on the k8s API and optimizes performance.

Acceptance Criteria

• Implement a Kubernetes cached client for querying Terraform objects
• Verify reduced pressure on the k8s API

[squaremo]

Rewriting as a (controller-runtime) controller with a manager will solve this by default (see #722 for discussion).