chore: 1. update bump k8s-version stable to 1.26.6

[FaGru3n]

• version bump to next version 1.26.6
• updates Upgrade stable to k8s version 1.27.3 if 1.25.x will retire on 2 January 2024 eclipse-tractusx/sig-infra#352

Testing

• checkout branch
• terraform init (optional)
• terraform plan
• validate changes

Additional information Terraform output

Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the following symbols:
  ~ update in-place

Terraform will perform the following actions:

  # module.stable_cluster.azurerm_kubernetes_cluster.aks_cluster will be updated in-place
  ~ resource "azurerm_kubernetes_cluster" "aks_cluster" {
        id                                  = "/subscriptions/899135fc-19c6-47cb-82f1-0230af7b99b5/resourceGroups/cx-stable-rg/providers/Microsoft.ContainerService/managedClusters/cx-stable-aks"
      ~ kubernetes_version                  = "1.25.6" -> "1.26.6"
        name                                = "cx-stable-aks"
        tags                                = {}
        # (23 unchanged attributes hidden)

      ~ default_node_pool {
            name                         = "default"
          ~ orchestrator_version         = "1.25.6" -> "1.26.6"
            tags                         = {}
            # (21 unchanged attributes hidden)
        }

        # (3 unchanged blocks hidden)
    }

Plan: 0 to add, 1 to change, 0 to destroy.

[almadigabor]

LGTM